Skip to main content

Full text of "Biology and Human Welfare"

See other formats

















! J 
i s 

I 

I ! 

N 





American Foundation 
ForTheBundwc. 



f- L l ^ 



O 



Digitized by the Internet Archive 

in 2012 with funding from 

Lyrasis Members and Sloan Foundation 



http://archive.org/details/biologyhumanwelfOOjame 



BIOLOGY AND HUMAN WELFARE 





^% 








JlT 'Is 








li N " - 








l^vft '«■ \\ 








m, ' 








% — 








gg|||^ | /ffi& 


miife. 




HI 


9BS 


,.-%;;. 


" 


n 


ISKIHHb^H Hhekp 






Wt 


BE**. 






m H 

1 I 

si 


^■Lv' 








■■ ■. ■■:.' ■ ':■■ ■■■■■■■■.-. ■ ' ■ ' 


-*^^ 






Ik .^l 







Louis Pasteur, chemist and biologist 
He saved more lives than Napoleon took in all his wars." 



BIOLOGY 

AND 

HUMAN WELFARE 

NEW EDITION 






BY 



JAMES EDWARD PEABODY 

FORMERLY HEAD OF THE DEPARTMENT OF BIOLOGY 

MORRIS HIGH SCHOOL 

NEW YORK CITY 

AND 

ARTHUR ELLSWORTH HUNT 

HEAD OF THE DEPARTMENT OF BIOLOGY 

MANUAL TRAINING HIGH SCHOOL 

BROOKLYN 



NEW YORK 

THE MACMILLAN COMPANY 

1933 






Printed in the United States of America • 



GlH- 



? 



fy 



^u> 



New Edition Copyrighted, 1933, 
By THE MACMILLAN COMPANY. 



Set up and electro typed. Published April, 1933. 



ALL RIGHTS RESERVED NO PART OF THIS BOOK MAY BE 

REPRODUCED IN ANY FORM WITHOUT PERMISSION IN WRITING 
FROM THE PUBLISHER, EXCEPT BY A REVIEWER WHO WISHES 
TO QUOTE BRIEF PASSAGES IN CONNECTION WITH A REVIEW 
WRITTEN FOR INCLUSION IN MAGAZINE OR NEWSPAPER 



Original Edition Copyrighted, 1924, 
By THE MACMILLAN COMPANY. 



Published February, 1924. 



PREFACE 

There are seven outstanding features of this New Edition of 
Biology and Human Welfare: (1) The emphasis on the vital 
relations of biology to human welfare ; (2) the new material that 
has been introduced ; (3) the possible adjustment of the contents 
of the book to different courses in biology ; (4) the combination of 
text and laboratory outlines in a single book ; (5) the unit-problem 
arrangement of its material ; (6) the illustrations, questions, and 
applications; and (7) the constructive criticism of many experts 
in the field of biology. 

1. In the teaching of high-school biology in former days the 
principal emphasis was laid on details of external and internal 
structure and on classification of plants and animals. Somewhat 
later a study of the functions of living organisms became the core 
of biological teaching. While of course all of these aspects must 
receive due consideration in a biological course, the authors believe 
that high-school boys and girls find greater interest and benefit in 
considering the applications of this subject to human welfare. 
Scientists are learning more and more ways to counteract the 
effects of harmful plants and animals and to develop those organ- 
isms that minister to everyday living. Flowering and flowerless 
plants, mammals, birds, fishes, insects, and protozoans furnish 
a wealth of material for studies that naturally appeal to ado- 
lescents. Problems relating to these groups of living things 
occupy a central place in this text. Other problems are suggested 
in the questions and applications at the end of each of the units. 

2. A large amount of wholly new material has been added in this 
New Edition. In Problem 1 of Unit I we have presented ma- 
terial for study which we are confident will at once arouse the 
interest of the students, show them some of the essentials of the 
scientific method of discovery, and emphasize a few of the more 
striking relations of biology to human welfare. The newer knowl- 
edge of osmosis and nutrition has been introduced in Units III 
and VI. In Unit VII, Problems 4 and 5, we have discussed the 



vi PREFACE 

racial history and the modification of plants, animals, and man 
with sufficient detail to meet the requirements of most of the 
second-year syllabi. .The classification of plants and animals and 
the study of a rather wide range of flowerless plants and of addi- 
tional vertebrates and invertebrates will be found in Units VIII 
and IX. We have included in Unit X a discussion of success in 
life as the logical culmination of biological study. 

3. The authors sent a questionnaire to the Commissioner of 
Education in each of the forty-eight States of the Union. All but 
two returned very helpful answers and in many cases complete 
outlines of biological courses. A tabulation of these returns shows 
that while in many communities biology is taught in the first year 
of the high school, in general it seems to be a second-year course. 
The material presented in this book is suitable in character and 
sufficient in quantity to meet both of these needs. If the students 
who take the course have had little or no biology, emphasis might 
best be laid upon the fundamental principles of nutrition (Units 
I-VI), of reproduction (Unit VII, but omitting Problems 4 and 5), 
and upon the relations to human welfare of bacteria, mammals, 
birds, and insects (see Units VIII and IX). If, on the other hand, 
a considerable number of these topics have been presented in 
general science or in an elementary course in biology, a more 
detailed study should be made of the classification, structure, 
history, and modifications of living organisms (see Units VII-IX) 
and of man in relation to his environment (Unit X) . 

4. The authors have become more and more convinced that a 
course in biological science that does not include a considerable 
amount of individual laboratory work and classroom demonstra- 
tion is a misnomer. Many teachers choose to prepare their own 
laboratory directions to meet special conditions. Other enthusi- 
astic teachers of the subject who do not have sufficient training, 
experience, or time at their disposal find specific suggestions very 
helpful. To those teachers who are using the laboratory direc- 
tions for the first time it is suggested that it would be advisable 
to plan the laboratory work several weeks in advance, since in 
some cases that amount of time will be needed to get the living 
material ready. The exercises we have included in this book (and 
the text as well) are the outcome of many years of actual trial in 
a considerable number of classrooms ; they have been repeatedly 



PREFACE vii 

mimeographed and revised ; and in their present form have been 
found to work successfully even with large groups of students. 
The directions and the questions in each exercise are clearly 
stated and logically arranged ; when carefully followed they aid 
the student, with a minimum of direction on the part of the 
teacher, to come into first-hand contact with worth-while bio- 
logical material. As a result the student's eyes should be opened 
to the fascinating processes going on in the world about him and 
to the functions and adaptations of his own body. At the same 
time he acquires the elements at least of real scientific observation 
and reasoning. 

5. The Unit-Problem arrangement of material has been adopted 
throughout the study of plants, animals, and man. In this plan 
of presentation it has been found possible to emphasize, even more 
fully than in the 1924 edition, the essential similarities in the 
biological functions of all living things, however much these 
organisms may differ in structure. While it is entirely possible 
to change the order in which the successive Units are to be studied, 
the authors believe that the Problems comprised in a given Unit 
should in the main be considered together. Exceptions, however, 
might well be made in the study of flowers, insects, and birds, 
which, of course, should be studied whenever suitable material is 
available. 

Units I-VI contain a comparative study of the nutritive func- 
tions of plants, animals, and man ; and Unit VII a study of the 
essential principles involved in the process of reproduction. In 
preparing the studies just mentioned the authors have selected 
the relatively few types that seem best to serve this purpose, 
reserving to later Units a consideration of these functions in the 
other plants and animals studied. This plan, we believe, insures 
far more unified impressions in the minds of students than would 
the survey of a wide field of more or less unfamiliar forms. 

6. For this New Edition we have taken special care to select 
illustrations that have obvious teaching value. Most of the 
pictures are new, and practically all of the diagrams have been 
redrawn and relabeled. A few pictures have been introduced 
because of their special attractiveness. We have emphasized 
the pedagogical significance of most of the illustrations, either by 
placing comments or questions beneath them, or by referring to 



viii PREFACE 

them in the Questions and Applications at the close of each of the 
Problems. 

In order to assist the student to emphasize and fix in his mind 
the high points in each problem we have inserted lists of questions 
and applications. Many of these questions can be answered from 
the laboratory work that has been done and from the text. A con- 
siderable number, however, have been included for the purpose 
of stimulating the student to carry on additional investigation 
and reading. Several types of tests — direct question, multiple- 
choice, and completion — will be found in the various groups. 
We believe it wiser to place all of them at the close of the various 
Problems, rather than to interrupt the sequence of the studies. 



ACKNOWLEDGMENTS 

It is impossible for the authors to express in any adequate way their 
appreciation for the generous help given us by the experts in their various 
fields in Boston, Cambridge, Albany, New York City, Washington, 
Chicago, and Denver. In the preparation of the sections relating to 
alcohol, for instance, we have had personal conferences with over 50 of 
the widely recognized authorities in medicine, biology, education, life 
insurance, government, and social service. Their helpful counsel has 
enabled us to prepare a treatment of this subject which we believe will 
appeal to the intelligence of adolescents. We are also deeply indebted 
to the experts in the Federal Departments in Washington for a careful 
checking up of our statements on birds and mammals (Dr. W. B. Bell 
and his assistants in the Biological Survey), insects (Dr. L. 0. Howard, 
Dr. F. C. Bishopp, and other members of the staff of the United States 
Bureau of Entomology), plants (Dr. F. V. Coville and other experts in 
the Bureau of Plant Industry), fishes (three members of the Bureau of 
Fisheries), forests (Dr. W. N. Sparhawk). These men have also supplied 
us with valuable illustrations. 

The whole manuscript has received the helpful criticism of Dr. C. 
Stuart Gager, Director of the Brooklyn Botanic Garden, of Miss Elsie 
Kupfer, Head of the Department of Biology, Wadleigh High School, 
New York City, and of Mr. Harold E. Foster, formerly Head of the 
Department of English of the Morris High School, New York City. 
Dr. William H. Park, Director of the Laboratories of the New York Board 
of Health, and Dr. Charles F. Bolduan of the Department of Health have 



ACKNOWLEDGMENTS ix 

given valuable assistance in the Problems relating to health and disease. 
To Dr. F. S. McKay, to Dr. Thaddeus Hyatt of the Metropolitan Life 
Insurance Company, and to Dr. Frederick B. Noyes, Dean of the Dental 
School of the University of Illinois, we are indebted for generous help in 
preparing the text on teeth. 

The authors wish especially to express their gratitude to Dr. Walter 
B. Cannon and Dr. W. J. Crozier for the use of a laboratory room in the 
Harvard Biological Institute during the past year, and to Dr. George 
Howard Parker, Dr. William M. Wheeler, Dr. Robert H. Woodworth, 
and Dr. C. T. Brues of the biological staff of Harvard University for their 
generous help. The following have also given us much assistance : 
Dr. Clarence W. Hahn, Head of the Department of Biology, High 
School of Commerce, New York City ; Dr. W. T. Hornaday, formerly 
Director of the New York Zoological Park; Dr. Frank M. Chapman 
of the American Museum of Natural History; Dr. Herbert E. Walter 
of Brown University; Dr. Reid Hunt, Dr. Walter B. Cannon, and Dr. 
Percy G. Stiles of the Harvard Medical School ; Dr. Thorne M. Carpenter 
of the Carnegie Nutrition Laboratory; Dr. Harry Emerson Fosdick of 
the Riverside Church, New York City; Judge Charles L. Hibbarcl of 
Pittsfield, Mass.; Dr. H. H. Goddard of the Ohio State University; 
Mrs. Katherine Bruderlin Crisp of the East High School, Denver, 
Colorado ; Miss Christine Dunnet of the Manual Training High School, 
Brooklyn, New York ; Brigadier-General J. R. Kean (Retired) of the Army 
Medical Museum, Washington; Mr. C. B. Hubbell, Statistician of the 
Massachusetts Registry of Motor Vehicles; Dr. Caroline Latimer of 
Baltimore ; Mrs. Walter Reed of Washington ; Mr. John R. Kissinger of 
Huntington, Illinois ; Dr. W. R. Redden, Director, First Aid, and Captain 
Charles B. Scully, American Red Cross ; the biology teachers who kindly 
prepared lists of reference books; and especially the teachers in the 
Manual Training High School, Brooklyn, and in the Morris High School 
of the Bronx, New York. 

We count ourselves most fortunate in being able to include illustrations 
specially autographed for this book by President Franklin Delano Roose- 
velt, by the late Chief Justice William H. Taft of the Supreme Court 
of the United States, by the late Charles W. Eliot, former President of 
Harvard University, and by Miss Helen Keller. Most of the illustrations 
credited to Brooklyn Botanic Garden have appeared in Gager's Funda- 
mentals of Botany and General Botany (P. Blakiston's Son & Co., Phila- 
delphia), and are here reproduced with the permission of the author. 
For their generous permission to use illustrations we are deeply indebted 
to the American Museum of Natural History, the New York Zoological 
Society, the Department of Agriculture in Washington, Science Service, 
Washington, Miss Cornelia Clarke of Grinnell, Iowa, the National 



x ACKNOWLEDGMENTS 

Tuberculosis Association, the American Child Health Association, the 
World Book Company, the American Red Cross, Perkins Institution for 
the Blind, the National Association for the Blind, Clarke School for the 
Deaf, the Massachusetts General Hospital, the Army Medical Museum of 
Washington, the Connecticut Agricultural Station, and the New York 
State Agricultural Station at Geneva. 

J. E. P. 
A. E. H. 
March 25, 1933. 









TABLE OF CONTENTS 

PAGE 

UNIT I. A PREVIEW OF BIOLOGY 1 

Problem 1. How Is Human Knowledge Acquired? . . 1 
Problem 2. What Is the General Structure of Living 

Things? 12 

UNIT II. COMPOSITION AND MANUFACTURE OF 

FOODS AND PROTOPLASM 29 

Problem 1. What Is the Composition of Foods? ... 29 
Problem 2. How Are Foods Manufactured and Assimi- 
lated by Plants? 48 

UNIT III. HOW FOODS ARE PREPARED FOR USE IN 

LIVING THINGS 73 

Problem 1. How Are Foods Prepared for Distribution 
and Use in Plants? . . . . . . . .73 

Problem 2. How Are Foods Prepared for Distribution 
and Use in the Human Body? 91 

UNIT IV. HOW THE NEEDS OF CELLS ARE SUPPLIED 113 
Problem 1. How Is Circulation Carried On in the Human 

Body? 113 

Problem 2. How Are Plants Adapted for Transfer of 
Materials? 137 



UNIT V. RELEASE OF ENERGY IN LIVING THINGS 
Problem 1 . How Are Living Things Able to Do Work ? 
Problem 2. How Is Breathing Carried On in Man? . 

UNIT VI. WHAT WE SHOULD EAT AND WHY . 

UNIT VII. REPRODUCTION OF LIVING THINGS . 
Problem 1. How Do Animals Reproduce? . 
Problem 2. How Do Plants Reproduce? 



158 
158 
170 

188 

209 
209 
221 



xii TABLE OF CONTENTS 

PAGE 

Problem 3. How Is Plant Propagation Carried On? . . 239 

Problem 4. How Are Plants, Animals, and Man Modified? 252 
Problem 5. How Do We Learn the History of Living 

Things? 283 

UNIT VIII. PLANTS AND HUMAN WELFARE . . 292 

Problem 1. How Are Plants Classified? .... 292 
Problem 2. How Are Flowering Plants Related to Human 

Welfare? 297 

Problem 3. How Are Flowerless Plants Related to 

Human Welfare? 323 

Problem 4. How Are Bacteria Related to Human 

Welfare? 339 

UNIT IX. ANIMALS AND HUMAN WELFARE . . 380 
Problem 1. How Are Animals Classified? .... 380 
Problem 2. How Are Mammals Related to Human Wel- 
fare? . 385 

Problem 3. How Are Birds Related to Human Welfare ? . 400 
Problem 4. How Are Reptiles and Amphibia Related to 

Human Welfare? 429 

Problem 5. How Are Fishes Related to Human Welfare? 450 
Problem 6. How Are Insects Related to Human Welfare? 474 
Problem 7. How Are Crustacea Related to Human Wel- 
fare? .522 

Problem 8. How Are Other Animals Related to Human 

Welfare? . . 532 

UNIT X. MAN IN RELATION TO HIS ENVIRONMENT 553 

Problem 1. How Are Protection and Locomotion Secured? 553 

Problem 2. How Are Our Bodies Controlled ? . . . 569 

Problem 3. Upon What Does Success in Life Depend? . 609 

Suggested List of Reference Books in Biology . . . 626 

Suggestions for Teachers of Biology 632 

Index 641 



BIOLOGY AND HUMAN WELFARE 



BIOLOGY AND HUMAN WELFARE 

UNIT I. A PREVIEW OF BIOLOGY 
PROBLEM 1. HOW IS HUMAN KNOWLEDGE ACQUIRED? 

How a child acquires knowledge. If you could look 
back to the earliest days of your childhood, you might be 
able to recall your first experiences in gaining knowledge of 
the world about you. You might remember the way you 
secured your food, your first sensations of pleasure and pain, 
your first consciousness of the distinction between good- 
tasting and bad-tasting substances, light and darkness, 
pleasant sounds and terrifying noises. All this earliest 
knowledge you acquired through your five senses — touch, 
taste, smell, sight, and hearing. 

In those early days your range of knowledge was, of course, 
very limited. But as you were able to get out of your crib, 
move about your home, and thus get in touch with the larger 
world outside, the knowledge you gained through your senses 
increased rapidly. Then, too, you learned to apply this 
knowledge in seeking to secure those things or those condi- 
tions that would contribute to your well-being as well as 
to avoid those that caused discomfort or pain. 

You have now become more or less familiar with the 
processes by which knowledge is gained, not only from direct 
contact with the world about you, but also from the printed 
page. Your opportunities to widen the boundaries of your 
knowledge are greater than they have ever been before. 
Your duty to do so is correspondingly greater. The wealth 

l 



2 A PREVIEW OF BIOLOGY 

of literature and science, of art and music is yours for the 
seeking. In no other country is education provided so liber- 
ally as it is in your own country. This opportunity for self- 
culture can be made yours, however, only through your own 
individual activity. 

How the human race has acquired knowledge. Just as 
the range of knowledge is very limited in the early years of 
childhood, so too the amount of knowledge possessed by the 
human race in its infancy was relatively small, and often 
this so-called knowledge was wholly incorrect. Less than five 
hundred years ago, for instance, most people believed that 
the earth was flat, that it was the center of the universe, and 
that the stars were hung from a dome above the earth. 
Disease was commonly regarded as a visitation of the wrath 
of the gods upon man for his sins, or as the work of evil 
spirits ; hence the cure of disease was sought through 
appeasing these spirits by superstitious rites. 

Gradually, however, men made more and more careful 
observations and drew more logical conclusions. For instance, 
men noticed that when ships pass out to sea, first the hulls 
disappear from the sight of the observer on land, then the 
sails, and finally the tops of the masts. These observations 
led men to question the belief that the earth was flat ; and 
after Magellan (111. p. 3) 1 had completed the circumnaviga- 
tion of the earth, mankind generally accepted this as final 
proof that our earth is spherical in shape. 

A similar development may be perceived in the ideas men 
have held in successive centuries with regard to disease and 
methods of treatment. If you were to consult the writings 
of the leading physicians of even a hundred years ago, you 
would be struck by the strange ideas then held. For instance, 
malaria was commonly believed to be due to the air breathed 

1 111. and p. are used throughout to mean illustration and page respectively. 



ACQUIRING HUMAN KNOWLEDGE 



in from swampy districts. During yellow-fever epidemics 
cannon were fired off and rattlesnake poison was adminis- 
tered to the fever patients. 

When, however, Pasteur 
(frontispiece) performed his 
epoch-making experiments 
toward the middle and close 
of the last century, there 
followed a complete revolu- 
tion in the treatment of 
disease, and modern pre- 
ventive medicine was born. 
During recent years such 
rapid progress has been 
made that we have high 
hopes that smallpox, diph- 
theria, typhoid fever, mala- 
ria, yellow fever, and even 
tuberculosis may largely 
disappear from the face of 
the earth. Much still re- 
mains to be done, however, 
before humanity can be freed from the ravages of cancer, 
heart disease, kidney troubles, and mental ailments. 

The scientific method of obtaining knowledge. We are 
now ready to consider the difference between the older 
methods by which mankind acquired knowledge and modern 
scientific methods. You have all seen the poles outside the 
barber shops with their red and white stripes ; but how 
many of you have ever wondered how such signs came to 
be used? Do you know that many diseases, for example 
pneumonia, were formerly believed to be due to the presence 
of mysterious " humors " in the blood ; that the way to get 




Fernando Magellan 

Portuguese navigator ( 1 480 ?- 1 5 2 1 ) . What 
problem did Magellan finally solve ? 



A PREVIEW OF BIOLOGY 



rid of these humors was by bleeding the patient ; and that 
this bleeding was done by barbers? Barbers, too, were 
employed to dress wounds. It is easy, then, to understand 
the origin of the white and the blood-red stripes on the 
barber poles of the present day ; for they formerly adver- 
tised the bandages before and after they had been used. 

What a contrast there is between this crude and wholly 
mistaken method of surgery and our modern methods ! If 




Courtesy of The Massachusetts General Hospital 

The Massachusetts General Hospital 

Exterior of the old building which is still in use. Note the "ether dome " at the top. 
(See illustration on opposite page.) 

you were to visit a hospital of this century (111. p. 10), you 
would find the most scrupulous cleanliness everywhere evi- 
dent. Before a surgeon performs an operation he cleanses 
his hands very carefully and puts on sterilized clothing and 
sterilized rubber gloves. Every instrument that is used has 
been likewise freed from germs. The result is that the death 
rate, even after serious operations, has become surprisingly 
low. How has mankind been able to acquire this wonderful 
knowledge? The answer will be found in the countless 
experiments performed, the observations made, and the 
conclusions drawn by our scientists. As an example of 



ACQUIRING HUMAN KNOWLEDGE 5 

modern methods of acquiring scientific knowledge, let us see 
how the cause of malaria and the method of its transmission 
were determined. 

Ideas formerly held as to the cause of malaria. Until 
comparatively recent times malaria was supposed to be due 




Courtesy of The Massachusetts General Hospital 

The Massachusetts General Hospital 

Interior of the " ether dome," where on October 16, 1846, was given the first 
public demonstration of anaesthesia to the extent of producing insensibility to pain. 
Sulphuric ether was administered by William T. Morton, a Boston dentist. The appa- 
ratus he used and the surgical instruments used by Dr. John C. Warren are now in the 
glass case beneath the row of photographs. 

to some ague or miasma that came from foul air, especially 
the air found in swampy regions — hence the name 
malaria (from two French words, meaning bad air). These 
earlier observers were right, as we now know, in associ- 
ating this disease with swampy regions, but they were 
wrong in thinking that malaria was due to anything in the 
air itself. Certain of their observations, therefore, were 
more or less correct, but their conclusions were incorrect 



6 A PREVIEW OF BIOLOGY 

because of lack of experimental evidence. We shall now 
see how it was proved that this disease is due not to 
swampy air, but rather to a microscopic form of life which 
is transmitted by a certain kind of mosquito that lives in 
swampy regions. 

How it was proved that malaria is not due to " swampy 
air." " It was early observed that ' malaria ' was apt to be 
prevalent during the damp and rainy seasons, and that it 
occurred principally in exactly such places as are now known 
to furnish ideal breeding grounds for the malaria mosquito. 
That new cases of malaria appeared at the time of year 
when the Malaria Mosquito abounded, was also recorded 
long before it was suspected that the insect was in any way 
connected with the malady ; and one of the old medical 
writers mentions as a characteristic of malaria seasons that 
' gnats and flies are apt to be abundant.' . . . ni 

In the last part of the nineteenth century the following 
experiments were carried on by scientists who spent the 
fever season in the dreaded malarial district in the swampy 
regions near Rome. They built for themselves a carefully 
screened house, in which they remained from sunset to sun- 
rise, since the malarial mosquito bites only during the night. 
In the daytime, however, they went freely among those who 
were stricken with the malarial fever, they allowed them- 
selves to be soaked with the falling rains, and at night they 
permitted the air from the swamps to come freely into their 
screened sleeping quarters. But while hundreds of malaria 
cases were all about them, none of these men contracted the 
disease. These experiments, therefore, proved that this dis- 
ease cannot be caused by bad air or by contact with people 
who have malaria. 

1 From " The Malaria Mosquito," by B. E. Dahlgren, published by The Ameri- 
can Museum of Natural History, New York City. Used by permission. 



ACQUIRING HUMAN KNOWLEDGE 



How it was proved that malaria is transmitted by a certain 
kind of mosquito. In connection with these experiments in 
Italy that we have just described a different kind of experi- 
ment was tried. Mosquitoes which had bitten malaria 
patients were caught and sent to London in a small wooden 
box. The hungry mosquitoes were then set free, and two 
London doctors allowed the mosquitoes to bite them. 
Eighteen days later both doctors developed malaria, although 
previous to this infection neither doctor had in any way 
suffered from this disease. Here, then, was experimental 
proof that it was the mosquitoes that transmitted the 
disease from Italy to 
London. 

How scientists dis- 
covered the germs 
that cause malaria. 
One of the wonderful 
stories of microscopi- 
cal investigation is 
that which recounts 
the steps by which 
it was proved that 
malaria never occurs 
except as the result 
of the bite of a cer- 
tain kind of mosquito 
— namely, the female 
Anopheles (a-nof'e- 
lez). (See 111.) The 
first step in this proof was taken in 1880 when Major Laveran 
(lav'raN'), a French military surgeon on duty in northern 
Africa, found that certain microscopic germs were always 
present in the blood of malaria patients. In 1898 Major 



Wing muscles 




Salivary glands -.. 



Courtesy of the American Museum of Natural History 

Model of a section of the female Anopheles 

mosquito 

For further illustrations relative to malaria see p. 548. 



8 A PREVIEW OF BIOLOGY 

Sir Ronald Ross, an English Army medical officer in India, 
proved the presence of germs, like those Laveran had found, 
in the body of the female Anopheles mosquitoes which had 
bitten people sick with malaria. These germs were also 
found in the blood of the two London doctors who were bitten 
by the infected mosquitoes sent from Italy. Try to imagine 
the careful work that Laveran and Ross must have done to 
discover these tiny germs ! (See pp. 547, 549 and 111. p. 548.) 

How the female Anopheles mosquito transmits the germs 
of malaria. A long series of investigations later showed 
that when the female Anopheles bites a malaria patient, she 
swallows, with the blood she sucks in, the same kind of 
germs that Laveran had discovered. After a time some of 
these germs escape through the wall of the mosquito's 
stomach and finally reach her salivary glands (111. p. 7). 
Hence, when she comes to bite a new victim, she injects with 
her saliva some of the malaria germs. If conditions are now 
favorable in the individual bitten, these germs cause the 
malarial chills and fever. 

What are the essential characteristics of a scientific 
experiment? We now see that modern methods of gaining 
scientific knowledge require (1) that there be a definite 
problem to be solved ; (2) that each experiment be per- 
formed with great care so that errors may be eliminated ; 
(3) that the observations be accurately noted ; and (4) that 
the right conclusions or inferences be drawn from the experi- 
ment. The experiments we have been describing are, of 
course, far too difficult for any but well-trained scientists to 
undertake. But there are many experiments of a simpler 
nature which the beginner in science may carry to a success- 
ful conclusion, if he uses the same general methods employed 
by more skillful workers in science. Such simple experi- 
ments are the following. 



ACQUIRING HUMAN KNOWLEDGE 9 

EXERCISE 1 

Does air occupy space ? Laboratory demonstration or home experi- 
ment. 

Invert a tumbler in a glass dish containing water about three inches 
deep, and press the tumbler down to the bottom of the dish. 

(The problem stated: To determine whether air occupies space.) 

1. (Preparation.) State what you have done. 

2. (Observation.) From your everyday knowledge state what 
filled the apparently empty inverted tumbler. 

3. (Observation.) How does the level of the water inside the 
tumbler compare with the level of the water on the outside of the 
tumbler ? 

4. (Conclusion.) What evidence have you from this experiment 
that the air in the tumbler occupies space ? 

EXERCISE 2 

Does air exert upward pressure? Laboratory demonstration or 
home experiment. 

Fill a tumbler full of water and cover it with a piece of paper, press- 
ing down on the paper with the palm of the hand. Remove the hand, 
and quickly invert the tumbler of water. (It is best to perform this 
experiment over a sink.) 

(The problem stated: To determine whether air exerts an upward 
pressure.) 

1. (Preparation.) Describe what you have done. 

2. (Observation.) State what you observed. 

3. (Conclusion.) What evidence have you that air exerts an up- 
ward pressure? 

Other examples of scientific investigation. You should 
know that a scientist reaches his conclusions only after the 
most painstaking experiments and observations. If you 
were to visit the Department of Agriculture in Washington, 
the Lick Observatory in California, the General Electric 
Works at Schenectady, or the Rockefeller Institute for 
Medical Research in New York City (111. p. 10), you would 



10 



A PREVIEW OF BIOLOGY 



be completely bewildered by the complexity of the scientific 
instruments that you would see. With these instruments 
the science workers can measure accurately the inconceivable 
distances to the remote stars and the velocity of light ; they 
can watch the movements of germs so small that they will 
pass through a filter made of porcelain ; and they can deter- 




Courtesy of the Rockefeller Institute 

The Rockefeller Institute, New York City 
Here important researches are carried on with reference to plants, animals, and man. 

mine the characteristics and chemical composition of particles 
of matter, even those found in the sun and the stars. 

The various sciences that are related to human welfare. 
The word " science " is derived from the Latin word scio, 
which means I know. After our discussion in the following 
chapters you will understand more completely the definition 
of science as given in the Century Dictionary. " Science is 
the knowledge gained by systematic observation, experiment, 
and reasoning." It includes a great number of facts and 



ACQUIRING HUMAN KNOWLEDGE 11 

principles. For this reason and for convenience of study we 
separate science into different departments. Some of these 
we shall now consider briefly, and we shall show some of the 
relations of these departments of science to human welfare. 

Astronomical science or astronomy treats of the heavenly 
bodies, their relative size, their enormous distances from us, 
from the sun, and from one another, and their movements 
through space. Mariners, even in these days of complicated 
instruments, still plot their course over the sea by observing 
the sun by day and the stars by night. The daily rise and 
fall of the tides result from the changing position of the 
moon with reference to the earth. 

Physics is the science that includes the study of the 
various forces that operate in the universe. Among these 
forces are light, heat, electricity, and magnetism. Think 
how many of these forces we now can harness for our use in 
heating and lighting our houses, in traveling by train, 
automobile, or airplane, and in sending and receiving 
messages by telegraph, telephone, or wireless. 

Chemistry treats of the composition of lifeless and of living 
things. It teaches us how a fire burns, how soap cleanses 
our hands and clothes, how foods, medicines, and dyes can 
be manufactured, and how poisons can be detected. 

Biology (from the Greek, bios meaning life and logos 
meaning study of) tells us about living things, namely, 
plants, animals, and human beings. Just as science was, 
for convenience, divided into the various special sciences, 
so biology itself may be further subdivided. When we 
confine our study to plants, we call this department of 
biology botany. Zoology is limited to the study of animals. 
Human biology (which is commonly but incorrectly called 
human physiology) takes up the study of the structure of the 
human body and various kinds of work that it can do, as 



12 A PREVIEW OF BIOLOGY 

well as the care, or hygiene, of the body. When we discuss 
the mental processes of man, we make a still further sub- 
division of human biology, and call this psychology, or 
study of the mind. 

QUESTIONS AND APPLICATIONS 

1. What caused people to think the world was flat? What reason have 
you for thinking otherwise except that you have been told the world is 
round ? 

2. What observations had physicians made a hundred years or more 
ago that led them to conclude that malaria was caused by swampy air? 
Were their conclusions wrong? Give reasons for your answer. 

3. How were scientists able to prove that "swampy air" was not the 
cause of malaria? What difference was there between the ancient and 
the modern experiments that led to such different conclusions ? 

4. How was it proved that a mosquito transmitted something that 
caused malaria ? At what personal risk was this knowledge gained ? 

5. Describe the work of Laveran and Ross in proving the real cause of 
malaria. 

6. Show that Exercise 2 as performed by you had the four character- 
istics of a scientific experiment. 

7. In connection with each of the following projects state which of the 
sciences would be especially involved : (a) installing a telephone ; (b) test- 
ing foods for impurities ; (c) treating a case of diphtheria ; (d) studying 
an eclipse of the sun ; (e) testing the intelligence of an individual ; (/) de- 
termining the economic importance of crows ; (g) investigating the best 
kind of crops to plant in a given field. 

PROBLEM 2. WHAT IS THE GENERAL STRUCTURE OF 
LIVING THINGS? 

The number and variety of living things in our environ- 
ment. Plants and animals form a very important part of 
our environment. Few people, however, have any con- 
ception of the myriad forms of living things that are in the 
soil, on the surface of the earth, in the water, and in the air. 
To most of us, it is true, fishes, birds, domestic and wild 







1 


Jgjf! 










4 « 


::^>: 


.' f" 








3r- 


vs 








&> '' TK 


IKak^ 


"i^H 






^^IKillL^^ . 






m S 
lllti 






* 










■5 * 




■ B 








> 1 


ii* 


1 


%'ll.-«l^' 


p^ilLi? •; ; "; 


1« ^mf 2 !! 


wk. tB 




-^Ed^SSE^lfc.. 



PTzoio &2/ Southern Pacific Co., Courtesy of U. S. Forest Service 

u Grizzly Giant " Sequoia tree, Yosemite National Park, California 

Compare size of the tree with the group of horses at the base of its trunk. The 
Sequoias are the oldest living things in the world, some of them having been sap- 
lings over 4000 years ago. 



14 A PREVIEW OF BIOLOGY 

animals, trees, and ordinary plants of the field are more or 
less familiar. But how many of us have any idea that the 
known kinds of insects number hundreds of thousands, and 
that even a brief description of the various kinds of grasses 
would fill a large-sized volume? More than this, the 
microscope has revealed a world of living forms wholly 
invisible to the naked eye, forms that were absolutely 
unknown to those who lived less than a century ago. 

Biology, then, includes not only the study of man, but 
also the study of all forms of plant life from the microscopic 




Modified, after Lull 

A sulphur-bottom whale and an African elephant, showing comparative size 
How many elephants might be crowded into this whale's body? 

germs in the air, earth, and water to the gigantic redwood 
trees of California (111. p. 13) that tower to a height of 300 
feet ; from invisible living animals that swarm in a drop of 
stagnant water to huge elephants and whales (See 111.). 

How living things differ from lifeless things. One might 
think that it would be an easy matter to state the charac- 
teristics that distinguish living things from lifeless things. 
Such is the case when we compare a rock in a field with a 
horse that is feeding beside it. Unlike the animal, the lifeless 
rock is unable to move itself, it neither eats nor breathes, and 
it gives no evidence that it possesses feeling or will power. 

But suppose we select for comparison a railroad loco- 
motive and a horse. Both move ; both need a plentiful 
supply of air ; both develop heat and the power to do work ; 



GENERAL STRUCTURE OF LIVING THINGS 15 

and both give off certain waste matters. The horse, we 
may say, requires food ; but so does the engine ; for coal 
and water are as necessary for the generation of heat and 
power in the engine, as food and water are for a similar 
purpose in the horse. 

When we try to state the characteristics that will dis- 
tinguish plants from all lifeless objects, we find the task still 
more difficult ; for most plants familiar to us do not move 
about from place to place, as do locomotives and automo- 
biles ; it is difficult to realize that plants give off heat ; and 
they give no evidence that they have conscious feelings as 
do the common animals. In spite, however, of all possible 
similarities, we are usually able to distinguish living from 
lifeless objects at least by the three following characteristics. 

In the first place, living things use some of the food they eat 
for growth. No one ever heard of an engine or other lifeless 
object beginning as a small machine, and then slowly growing 
larger until it comes to have many times its former weight. 1 
Yet this is what happens to all plants and all animals. The 
average child, for instance, at birth weighs six to eight 
pounds ; while a man's weight is over twenty times as great. 
And if we should try to compare the size and weight of an 
oak tree with that of an acorn from which it started, we 
would find the amount of increase to be enormous. 

In the second place, parts of a locomotive or of any other 
lifeless machine by continual use become worn or broken, 
and the engine must be sent to the machine shop for repairs. 
Our bodies, too, are being constantly worn away ; for every 
time we make a motion of any sort, some of the material in 
our bodies is used up ; every time we think or exert will 
power, some of the brain substance is probably changed into 

1 While it is true that icicles and other crystals apparently " grow," this kind of 
growth is brought about by the addition of material to the outer surface. 



16 



A PREVIEW OF BIOLOGY 



>Seeds 



dead waste material. But in contrast to lifeless machines, 
our bodies are self -repairing . The food that we eat not only 
goes to increase the size and weight of the body, but it also 
furnishes material to make good the wear and tear of every- 
day life. This power of self-repair is likewise present in all 

animals and in plants as 
well. 

A third characteristic 
that distinguishes living 
things from those that 
are lifeless is the fact 
that they produce plants 
or animals like them- 
selves. No lifeless ob- 
ject can do this. We 
shall find in our later 
study that, while appar- 
ently there are a great 
many different methods 
of producing these new 
organisms, still in their 
essential features these 
various methods of re- 
production are much the 
same. 
In brief, then, we may say that all living things have the 
power of growth from within, of self-repair, and of the reproduc- 
tion of their kind, while lifeless objects possess none of these 
powers. 

The parts of our common plants. Anyone who has 
allowed weeds to get the upper hand in his garden has often 
found that quite an effort is required to pull these weeds 
from the ground. If you have ever watched a large-sized 




ix&*r Ground /ere/ 



A complete bean plant 
Name six organs of this plant. 



GENERAL STRUCTURE OF LIVING THINGS 17 



-Eyepiece 



tree (111. p. 292), the branches of which are being tossed by a 
heavy wind, you must realize that a huge plant of this sort, 
even more than the smaller weed, is held in place by very 
efficient structures that cling to the earth. These under- 
ground parts of a 
plant we know as 
roots. 

You have ob- 
served, too, that 
plants which have 
not been watered 
for a considerable 
time wilt, and in 
periods of pro- 
longed drought die. 
If, however, water 
is poured upon the 
soil in sufficient 
quantity before too 
much water has 
been lost, these 
plants usually re- 
vive and continue 
their healthy 
growth. One sees, 
then, that the roots 
have a second use, namely, that of absorbing water and 
other materials from the soil. 

The parts of a plant that are probably more familiar to us 
are the stems and the leaves. In most of our common plants 
the stems of trees and of other plants are cylindrical in shape, 
and are divided into smaller and smaller branches. In this 
way the leaves that they bear become widely exposed to 







B- -Draw-tube 






Iffi^Hjfgj^. ^--—Coarse 
\ 10 Hi adjustment 


Body tube i 






Revolving 
nosepiece —__'>>« 
for two fm 
objectives /M§ 




tsnc ' mB^MBk- adjustment 

9 L'H-^lrw 


Objectives *~~~~ ~~[% 


Xmrnmn—*?- M&mm 


Staoe - 




Condenser — faQH^ 




mt Mirror- 4 
Object ''WM*. i 
holder fl A 


M Pillar 


^sk ■ 


Jr:i« Fooi 


Leeuwenhoek's 
microscope 




Modern microscope 



The microscope used by Leeuwenhoek, and a modern 
microscope (page 20) 



18 



A PREVIEW OF BIOLOGY 



the sun and air. During spring and summer blossoms or 
flowers appear on the branches. In fall-flowering plants the 
flowers appear in autumn as the days are growing colder, e.g. 
hardy asters, chrysanthemums, and goldenrod. Later these 
flowers develop fruits, containing seeds. Many people may 

not realize that some plants 
have both flowers and fruits, 
e.g. grasses, elm trees (111. 
p. 292), potato plants, and 
rubber plants. 

We see, then, that the 
plants with which we are 
most familiar have roots, 
stems, leaves, flowers, and 
fruits (111. p. 16). Some 
plants, however, are so 
simple in structure that 
they have no parts that can 
be called roots, stems, 
leaves, flowers, and fruits. 
As examples, we may name 
mushrooms (111. p. 336), 
bread mold (111. p. 335), 
yeast (111. p. 333), the single- 
celled plants known as bac- 
teria (111. p. 342), and the microscopic plants that form the 
thin, green layer you may have noticed on the trunks of trees, 
especially when the bark is exposed to the north in dense 
woods (111. p. 221). Even these simpler plants, however, 
must carry on their life activities, although in a somewhat dif- 
ferent way from the method followed by the higher plants. 

The parts of the human body and of animals. In the 
human body one can distinguish at least three regions: 




Anton van Leeuwenhoek, Dutch natu- 
ralist (1632-1723) 
This merchant of Delft, Holland, has 
been called " The Father of Microscopical 
Discovery" because of his observations 
on " animalcules " (page 20). 



GENERAL STRUCTURE OF LIVING THINGS 19 



namely, the head, containing the brain and the various 
sense organs ; the trunk, containing the heart, lungs, and 
the digestive organs ; and the neck, connecting these two 
regions. To the trunk are attached two pairs of jointed 
appendages (a-pen'da-j£z), that is, 
two arms and two legs. The eyes, 
the ears, and the nose enable us to 
receive impressions of sight, hear- 
ing, and smell from the world about 
us. With the hands we grasp ob- 
jects and do intricate pieces of work 
like writing, sewing, or typing. 

In contrast with the erect posi- 
tion of man we find that the bodies 
of turtles, birds, horses, and dogs 
are in a more or less horizontal 
position. These animals, however, 
have the three regions mentioned 
above, two pairs of jointed ap- 
pendages, and the sense organs 
situated in the head region. In 
addition, all these animals have 
tails. 

As we go down the scale of ani- 
mal life below the fishes, we find no 
jointed appendages, except in the 
great group to which insects, 
spiders, and crabs belong. When 
we study worms, coral-making animals, and sponges, we 
are unable any longer to distinguish head, neck, and trunk, 
and eyes and ears cannot be found. Finally, in each 
microscopic animal, the tiny bit of living substance seems 
at first sight to have no very definite parts by which it 




Courtesy of Army Medical Museum, 
Washington, D. C. 

Microscope of Robert Hooke 
English mathematician and in- 
ventor (1635-1703) (p. 21). 



20 



A PREVIEW OF BIOLOGY 



carries on its life processes of growth, self -repair, and re- 
production. 

Terms used in biology. We are now ready to make use of 
certain terms that will appear again and again in our study 
of biology. The definite parts of a living thing, be it plant, 
animal, or man, are known as organs. The organs of a 

plant, for instance, are the 
roots, stems, leaves, flowers, 
fruits, and seeds ; some of 
the organs of the human 
body are eyes, ears, arms, 
legs, heart, lungs. The defi- 
nite work carried on by an 
organ is known as its func- 
tion. Thus the function of 
the heart is to pump the 
blood through blood vessels, 
and that of the lungs is to 
take in fresh air and to give 
off the air that has been 
used. 

History of the study of 
the microscopic structure of 
living things. The study of 
plants and animals was car- 
ried on for centuries before 
the microscope was invented. Those earlier biologists, there- 
fore, had no knowledge such as we now possess in regard to 
the minute structure of living things. With the invention 
and development of the compound microscope (111. p. 17), 
however, a flood of light was thrown upon the problems of 
biology. 

Over two hundred years ago a Dutch naturalist, Leeuwen- 




Matthias Jakob Schleiden, German bot- 
anist (1804-1881) 

He elaborated the cell theory as related 
to plants and may with Schwann (p. 21) 
be called co-founder of this theory that has 
revolutionized our study of organic life. 



GENERAL STRUCTURE OF LIVING THINGS 21 



hoek (La'wen-hook') (111. p. 18), who lived from 1632 to 1723, 
constructed a crude instrument (111. p. 17) that enabled him 
to see tiny, hitherto invisible organisms in stagnant water. 
About the same time an English physician by the name of 
Hooke (1625-1703) used the microscope (111. p. 19) to study 
thin sections of cork (the 
bark of Spanish oak). He 
discovered that this plant 
material was composed of 
tiny compartments, each in- 
closed in thick walls. These 
compartments he called cells 
because of their resemblance 
in form to the cells of honey- 
comb. Other biologists 
later found that animal and 
human bodies are likewise 
made up of similar micro- 
scopical units or cells. 

These earlier investiga- 
tors laid special emphasis on 
the relative form and size 
of cells, and the cell walls, 
which inclosed the cells, 
were regarded as very im- 
portant. Gradually, how- 
ever, these scientists realized that the material inside the 
cells contained the real living substance. This living sub- 
stance was called by several names, but finally the name 
protoplasm (from the Greek, meaning first form) was uni- 
versally accepted. 

About the middle of the last century (1838) two German 
biologists, Schleiden (shli'den) (111. p. 20), who was working 




Theodor Schwann, German physiologist 
and anatomist (1810-1882) 
The author of the cell theory of organic 
structure and function and the first to apply 
experimental methods of the physicist to 
investigations of the animal machine. 



22 A PREVIEW OF BIOLOGY 

with plants, and Schwann (shvan) (111. p. 21), who was 
working with animals, developed rather fully the idea that 
all living things are composed of cells. This is known as the 
cell theory, and this theory forms the basis of all modern 
biology. 

The general structure of a cell. When a very thin section 
is cut from any part of a plant or animal and is examined 
under a compound microscope that magnifies as many as a 




"~i /'" 



:m. 



Cell wall |T Y 






■ ; V ..-^:;,.,r. : v: : .,..:..-.-- ...... 

— Ce/£ nucleus — -'-.---—»— 

— Cytoplasm '----•. v . ; , - - ^ ^ 



V-' 












Section, o/ceW Surface view of cell 

Diagrams of a cell 

Why is one able to see the cell nucleus and other bodies within the cell ? 

hundred times, the plant or animal cells of which the sec- 
tion is composed seem to have only length and breadth, and 
the cell walls appear as straight or curved lines (111. p. 26). 
When, however, one carefully raises or lowers the lenses of the 
microscope by focusing, it becomes evident that every cell 
has a certain depth or thickness (See 111.), and that walls 
inclose the cell, much as the peel covers an orange, or the 
sides, top, and bottom of a box inclose the contents. 

If the cells are treated with certain stains, a part of the 
content of each cell becomes more deeply dyed, and we are 
thus enabled to distinguish a dense and a less dense portion 
in the interior of the cell (See 111.). To the denser portion of 






GENERAL STRUCTURE OF LIVING THINGS 23 

the cell contents, usually more or less spherical in shape and 
commonly situated near the center of the cell, is given the 
name cell nucleus. In some kinds of cells the nucleus may be 
seen without the use of a stain. To the rest of the cell 
contents is given the name cytoplasm (si'to-plaz'm = cell 
plasm) . 

EXERCISE 3 

What is the microscopic appearance of plant cells? Laboratory 
study. 

1. Strip off from the layers, or thickened leaves, of the inside of an 
onion bulb pieces of the thin skin, or epidermis. Cut this into small 
pieces with scissors under water, and transfer a piece to a drop of 
iodine and water on a glass slide. Cover with a cover glass and ex- 
amine with the low power of the compound microscope. Make a 
careful drawing of three adjacent cells as they look when magnified 
100 or more times. Place beneath the drawing the general label. 
Cells from an onion membrane, considerably magnified. Label the 
parts of one of the cells : Cell wall, Cytoplasm, Cell nucleus. 

2. Mount a piece of the onion membrane on a slide in a drop of 
water without the iodine and examine under the compound micro- 
scope. What is the natural color of the cell body and the cell nucleus ? 

EXERCISE 4 

What is the microscopic appearance of certain cells of the human 
body? Laboratory study. 

1. Rub gently with a clean finger tip the mucous lining of the 
mouth. Stir the finger tip in a drop of iodine and water on a glass 
slide to remove the cells and cover them with a cover glass. Examine 
with the low and then with the high power of the microscope. Find 
several cells that resemble one another and make a drawing of one of 
them magnified either 100 or 500 times as the teacher directs. Label : 
Cell membrane. Cytoplasm, and Cell nucleus. Label the whole draw- 
ing, Cell from the lining of the human mouth, highly magnified. 

2. Mount some of the cells without the iodine in a drop of water and 
examine with the microscope, focusing carefully. What is the natural 
color of the cell body and the cell nucleus? 



24 A PREVIEW OF BIOLOGY 

Some of the characteristics of protoplasm. Protoplasm, 
when examined with the highest powers of the compound 
microscope, commonly appears as an almost colorless, semi- 
fluid substance, in which are often seen solid particles or 
granules which are probably tiny bits of food materials. 
The nucleus, as we have already said, is usually found near 
the center of the cell. The appearance and the composition 
of the protoplasm may be compared to that of raw white of 
egg. But in making this comparison, one should bear in 
mind that the white of an egg is not living substance. 
Biologists now understand a cell to be a bit of protoplasm, 
usually consisting of two parts, namely, a cell nucleus sur- 
rounded by cytoplasm; the two constituting the protoplasm. 
There may be no definite cell wall, but there is at least a 
limiting membrane covering the outside of the cell. 

How cell division is carried on. When a cell grows, the 
amount of protoplasm, of course, increases, and the cell itself 
grows. Were this process to continue indefinitely, cells 
would become large enough to be seen with the naked eye. 
This, however, does not ordinarily occur. For when the 
cell of a plant, of an animal, or of the human body reaches 
a certain size, the nucleus divides in two by a complicated 
series of changes (111. p. 25, A-I), and the halves of the 
nucleus separate to form two distinctive nuclei. Cell walls 
are formed between the two nuclei, and so the cytoplasm is 
divided into two parts, each having its own nucleus. These 
two cells in turn take in food, grow, and divide. In this way 
the number of cells increases with the growth of the plant, 
the animal, or the human being. 

Some of the tissues of the human body and of animals. 
When we pinch the hand, we feel the hard bones that form its 
skeleton. We can move the softer fleshy material, which is 
composed of muscles covered with skin. By clenching the 



GENERAL STRUCTURE OF LIVING THINGS 25 

fingers tightly, we can see and feel on the inner side of the 
wrist the tough cords or tendons of connective tissue which 
attach the muscles to the bones. As we pinch the hand we 










From Walter's " Vertebrate Zoology'' 

Stages in the division of a cell 

The star-shaped bodies in the cytoplasm are known as centrosomes ; they are 
important in the process of cell division in animal cells. Describe the successive 
changes that take place from Stage A to Stage I (a) in the nucleus, (b) in the cytoplasm, 
(c) in the centrosomes. The rod-shaped bodies are called chromosomes. 

have a sensation either of touch or of pain, and in this way 
we discover the presence of another of the tissues found in 
the structure of our hand, namely, nerve tissue. 



26 



A PREVIEW OF BIOLOGY 



All the parts of the hand we have been enumerating are 
known as tissues. In the hand we have found evidence of 





Ce//s from 

Nerve ce// frog's sk/n Musc/e ce//s 

Different types of animal cells 
What is the principal difference in the structure of these cells ? 

bone tissue, muscle tissue, connective tissue, and nerve tissue. 
Other kinds of tissue are also present in our bodies and in 
those of animals. Biologists have proved that each tissue is 
composed of cells, and that between these cells is material 

-^v;/:\:v>;y^' M *^^ made Dy tne ceils 

Group of two ft ; : ? 
cartilage cells -r'-j~~f 
Group of &-M^&**00M IM^Wlk:'C 



v ; ; ■■>:■■; 




Jour cells 

A cell --"""^ 

Nucleus 



Intercellular--^— , \^» 



Cartilage tissue 
Which parts are alive and which are lifeless ? 



called intercellular 
substance (for ex- 
ample, the hard part 
of bones and the 
elastic part of carti- 
lage or gristle) (111. 
at left). A tissue, 
therefore, may be 



GENERAL STRUCTURE OF LIVING THINGS 27 

defined as a building material of an organ, composed of cells 
of the same kind, together with more or less intercellular sub- 
stance that may be present. 

Some of the tissues of plants. The various organs of a 
plant are likewise composed of tissues. We have already 



Cell wall 
Cell sap 




Protoplasmic 
■""" membrane 



Epidermis cells 
from leaf 



Chlorophyll^ 
bodies 






—Protoplasmic 
membrane 



Palisade cells Pith cells Root cells 

from leaf from stem 

Different types of plant cells 

How do the walls of these cells differ ? In what one respect are the palisade cells 

different in structure from all the other cells ? 

studied onion membrane, which is a skin, or epidermal tissue. 
By dissecting the stem of a weed or the twig of a tree we find 
on the outside several layers that make up the bark. Within 
the bark is a stringy or woody material in which are tubes or 
ducts that carry sap, and in the center is soft pith. Pith is 
a plant tissue, and the bark and the wood are composed of 
several tissues. 



QUESTIONS AND APPLICATIONS 

1. Give some idea of (a) the number of kinds of living things, (b) the 
variations in size of plants and animals. 

2. State the three ways by which living things may be distinguished 
from lifeless objects. 



28 A PREVIEW OF BIOLOGY 

3. Name five of the parts of some common plant. Tell what work some 
of these parts perform. (See illustration p. 16.) 

4. Name some plants that are much simpler in structure than those 
referred to in Question 3. 

5. What are the three regions in man? What do two of these regions 
contain? (See illustrations pp. 94 and 117.) 

6 . What is the use of each of the two kinds of j ointed appendages of man ? 

7. Name four widely different animals that have regions similar to 
those in man. What additional region has each of these animals ? What 
takes the place of arms in each of the four animals ? 

8. What is meant by the terms organs and functions? 

9. What were the principal contributions of (a) Leeuwenhoek, 
(b) Hooke, (c) Schleiden, (d) Schwann? 

10. Why did Hooke give the name cells to the compartments in cork? 

11. Name and locate the three parts of a plant cell. (See illustration 
p. 78.) 

12. Why did we stain the cells when we studied them with the com- 
pound microscope? 

13. How is protoplasm like the white of an egg, and how is it different? 

14. How do the walls of the onion-skin cells differ from the cell mem- 
brane of the cells from the lining of the mouth ? 

15. In cell division what part of a cell divides first? What changes 
take place when the cytoplasm is dividing into two parts? 

16. Are tissues composed of cells of the same kind or of different kinds ? 

17. Name four tissues in your hand and tell how you are able to dis- 
tinguish each. 

18. What is intercellular substance? Give an example. 

19. Name two kinds of plant tissue and tell how these tissues differ 
from each other. 

20. What great advantage has a living machine, such as the human 
body, over a lifeless machine such as an automobile engine ? 

21. Make separate lists, as follows, of the living things alreadj^ familiar 
to you by actual observation in the vicinity of your home : (a) trees ; 
lb) wild flowers ; (c) vegetables growing in gardens ; (d) domestic 
animals ; (e) birds ; (/) insects. 

22. What instruments and what methods of treatment of cells have 
enabled modern biologists to achieve such success in their studies of cells? 

23. Locate in the leg and the wing of the next chicken or turkey you 
eat three of the tissues that are named in the text of this problem. 



UNIT II. COMPOSITION AND MANUFACTURE 
OF FOODS AND PROTOPLASM 

PROBLEM 1. WHAT IS THE COMPOSITION OF FOODS? 

Classes of Food Substances 

The sources of some of our foods. In the last unit we 
discussed briefly the structure and functions of the human 
body and of some familiar plants and animals. We turn now 
to a consideration of one of the primary needs of all living 
things, namely, that of food. 

Some of our foods come from certain parts of plants ; for 
example, potatoes, beans, onions, lettuce, apples, grapes, and 
grains of various kinds. Others are derived from animals ; 
for example, milk, butter, eggs, various kinds of meat, fish, 
and poultry. Is each of these foods composed of only one 
food substance, or are all of them combinations of two or 
more food substances? In the following experiments you 
should be able not only to answer this question, but 
also to gain some additional experience in the scientific 
method of gaining knowledge. 

EXERCISE 5 

Is flour composed of more than one kind of food substance ? Home 

experiment. 

Mix a tablespoonful of flour in just enough water to make a thick 
paste, tie it in a piece of cotton cloth or cheesecloth, and knead it for 
several minutes in a dish of water. Pour the water into a tumbler 
and allow it to stand for ten or fifteen minutes. 

1. Describe what you have done. 

29 



30 COMPOSITION AND MANUFACTURE OF FOODS 

2. Examine and describe the substance that settles in the glass of 
water. 

3. How does the material in the cloth differ in color and texture 
from the sediment in the glass ? 

4. What is your conclusion as to the composition of flour? 

EXERCISE 6 

Is milk composed of more than one kind of food substance ? Home 
experiment. 

1. Examine a bottle of milk that has stood undisturbed for a time. 
What is the difference between the color of the upper layer (cream) 
and the lower portion (skim milk) ? Is cream heavier or lighter than 
skim milk? How do you know? 

2. After pouring off the cream, add a spoonful of white vinegar or 
of lemon juice to two or three spoonfuls of the skim milk, boil the 
mixture, and strain through cheesecloth. Tell what you have done. 
How does the substance in the cloth differ in consistency both from 
the cream and from the skim milk? 

3. Heat a part of a spoonful of milk in a large, clean cooking spoon 
and hold over it an inverted clean, cold tumbler. Tell what you have 
done. What does the substance that you see collecting inside the 
tumbler seem to be like ? 

4. Heat a quarter of a teaspoonful of the skim milk in a clean cook- 
ing spoon until the liquid evaporates, and burn the solid residue until 
the black color disappears. State what you did. What is the appear- 
ance of the substance that is left? 

5. How many different kinds of substances have you found in milk? 
What is your conclusion from the four experiments ? 

Classes of food substances with examples. Proteins. 
In Exercises 5 and 6 you separated two common foods, flour 
and milk, into five substances, each of which is quite different 
from the others. In the flour experiment the material in the 
cloth is called gluten. The class of food substance to which 
gluten belongs is known as protein (pro'te-m) and gluten is 
wheat protein. It is the gluten in wheat flour that makes 
dough so sticky. In the milk experiment the substance in 



COMPOSITION OF FOODS 



31 



the cloth is called casein (ka'se-in) which is another kind of 
protein. Cream cheese consists largely of casein. Acids 
and the boiling process cause the casein in the milk to thicken 
or collect in solid masses. You are also familiar with the 
solidifying action of heat on the white of egg. White of egg 
contains a high per- 
centage of a kind 
of protein known as 
albumen. 

Starches. The 
white sediment that 
settled on the bot- 
tom of the glass in 
Exercise 5 repre- 
sents a second class 
of food materials. 
All the food sub- 
stances of this kind 
are known as starches. 
Starches, too, are 
named after the kind 
of plant from which 
each is derived. 
Thus we have wheat starch, cornstarch, potato starch. Each 
kind of starch is composed of grains quite different in shape 
from all other starches (111. above). 

Sugars. A third kind of food substance, very similar in 
chemical composition to the starches, is sugar. Sugars as 
well as starches are also commonly named after the plant 
from which each is obtained. For instance, we have cane 
sugar, beet sugar, maple sugar, grape sugar. Starches and 
sugars are grouped together in a class of food substances 
known as carbohydrates. 




Different forms of starch grains (highly magnified) 
How would the Board of Health be able to tell 
when cornstarch has been mixed with other kinds of 
foods ? 






32 COMPOSITION AND MANUFACTURE OF FOODS 

Fats. A fourth class of food substance is found in the 
cream of milk. Cream consists largely of a fat known as 
butter fat. Other fats which are known to you are lard from 
the pig, suet from the cow, olive oil from the olive fruits, and 
peanut butter from the peanut. 

Mineral matters. The ashes obtained by burning a small 
quantity of milk till all the black disappeared consist largely 
of phosphate of lime and carbonate of lime. These are both 
important substances belonging to a group of food sub- 
stances known as mineral matters. Table salt also belongs to 
this class. The method used to show the presence of mineral 
matters in milk may also be used to demonstrate the presence 
or absence of mineral matters in any food. It is difficult, 
however, to heat most foods sufficiently in an ordinary gas 
flame to cause all of the black substance to disappear. If the 
food is cut into thin slices, placed in a shallow cover, and the 
cover imbedded in the hot coals of a furnace for several hours, 
the black substance will in most cases all be burned. It will 
then be possible to remove the cover with tongs and to de- 
termine whether or not any ashes (mineral matters) are left. 

Water. The sixth kind of food substance that you found 
in your experiment with milk is water. There is only one 
kind of chemically pure water. Rain water is probably the 
nearest natural source of chemically pure water. If, how- 
ever, the air contains dust or smoke, the rain water will con- 
tain materials from these sources also. Drinking water 
usually contains one or more kinds of mineral matter in a 
very small percentage. The same method that you used to 
show the presence of water in milk may be used to show the 
presence or absence of water in any food. If, however, the 
food tested is a solid, it must not be heated hot enough to 
cause it to burn. The reason for this precaution will be made 
clear to you in Exercise 16. 



COMPOSITION OF FOODS 33 

Table of the Classes of Food Substances 



Classes 



Common Examples 



1 . Carbohydrates 

a. Starches . . 

b. Sugars . . . 

2. Fats . . . . 

3. Proteins . . . 

4. Mineral matters 

5. Water . . . . 



Wheat starch, cornstarch, potato starch 
Cane sugar, beet sugar, maple sugar, grape sugar 
Cream of milk, butter, lard, olive oil, peanut butter 
Casein of milk, gluten of wheat, albumen of egg 
Common salt, ash of milk, phosphate of lime 
Drinking water, water in meat, fruits, and vegetables 






Tests for the Food Substances 

How scientists have worked out methods of food analysis. 

In the above experiments simple methods were employed for 
separating the various food substances found in common 
foods. We are now to develop and use certain methods, or 
tests, by means of which the presence or absence of each of 
these substances can be indicated without this separation 
of the food substances. Now how were such tests de- 
rived? Most scientific discoveries are the result of years 
of investigation, and this is doubtless true of methods of 
analyzing and testing foods. In order to determine readily 
the presence or absence of a given food substance, it was 
necessary to find some definite means of distinguishing 
each of the food substances from all the others. That 
this is possible we shall now see. 

EXERCISE 7 

How can the presence of starches in foods be shown? Laboratory 
demonstration and home experiment. 

Put a small amount of one of the starches (for example, cornstarch) 
into a test tube, add a little water, shake thoroughly, and boil the 



34 COMPOSITION AND MANUFACTURE OF FOODS 




Proper method of holding a test tube 

Notice that a folded piece of paper surrounds 
the hot test tube just below the lip. The tube 
should point over the shoulder and not toward 
the face. Give reason for this direction. 

more fruits, one or more nuts, potato, 
in a table like the following : 



mixture. Allow the mixture to 
cool, and then add a few drops 
of iodine solution. 1 

1. State the preparation of 
the experiment and give your 
observation as to the color 
effect of iodine on corn- 
starch. 

Note (to be studied). 
Many experiments have 
shown that iodine has a color 
effect on all the starches simi- 
lar to the color effect on corn- 
starch. No other class of 
food substances is affected in 
color by iodine as are the 
starches. 

2. Write out the method 
you would use in testing a 
given food for starches. 

3. Test six or more com- 
mon foods, some derived from 
plants and some from animals 
(for example, milk, one or 
more cereals, eggs, one or 

parsnip). Record your results 



Foods Tested in Which Starch 
Was Present 



Foods Tested in Which Starch 

Was Absent 



1 Preparation of iodine solution. Dissolve in 10 teaspoonfuls (40 cc.) of water one 
half a teaspoonful (4 grams) of potassium iodide and one fourth this amount of 
iodine (1 gram). This solution, when thoroughly mixed, should be diluted to make 
one quart (1000 cc.). In a clean bottle this mixture will keep indefinitely. 



COMPOSITION OF FOODS 35 

EXERCISE 8 

How can the presence of reducing sugars in foods be shown? 

Laboratory demonstration or home experiment. 

Into a test tube put a small amount of grape sugar (a reducing 
sugar) ; add water and enough Benedict's 1 or Fehling's ! solution to 
make the mixture slightly blue. Boil the contents of the tube. 

1. State the preparation of the experiment and give your observa- 
tion as to the color effect of grape sugar upon the testing substance. 

Note (to be studied). Benedict's and Fehling's solutions contain 
a blue substance (copper sulphate, or blue vitriol) in which copper is 
present. When boiled with grape sugar, this blue substance is 
changed, or reduced, to a simpler yellow or copper-colored compound, 
which is insoluble and finally settles in the bottom of the tube. No one 
of the other classes of food substances affects these solutions as does 
grape sugar, nor do all of the sugars. The sugars which affect these 
chemical solutions in this way are known as reducing sugars. 

2. Write out a method you would follow in testing a given food 
for a reducing sugar. 

■3. Test six or more ordinary foods (for example, several fruits, 
a cereal, one or more vegetables, and milk) and record your results in 
a table like the following : 

1 Preparation of Benedict's solution. By using heat dissolve 173 grams of sodium 
citrate and 100 grams of sodium carbonate (anhydrous) in about 600 cc. of water. 
Pour the solution through filter paper into a glass graduate and add enough (distilled) 
water to make 850 cc. Dissolve 17.3 grams of copper sulphate in about 100 cc. of 
water, and add distilled water to make 150 cc. Pour the sodium citrate and sodium 
carbonate solution into a large beaker or battery jar and add the copper sulphate 
solution slowly, stirring constantly. 

Preparation of Fehling's solution. Dissolve 3 teaspoonfuls (34.64 grams) of pure 
pulverized copper sulphate (blue vitriol) in a little less than half a pint of water 
(200 cc). Make a second solution by dissolving in a pint (500 cc.) of water twelve 
heaping teaspoonfuls (150 grams) of Rochelle salt and 3 (5-inch) sticks of caustic 
soda (50 grams) . Fehling's solution does not keep for any great length of time and 
hence must be made up fresh a short time before it is needed. To do this, thoroughly 
mix two volumes of the copper sulphate solution and five volumes of the solution of 
Rochelle salt and caustic soda and dilute the mixture with an equal volume of water. 
It is more convenient to prepare it in small quantities using tablets that may be 
obtained from druggists. Before making any tests boil a small quantity of the 
Fehling's solution in a clean test tube. If it retains its transparent blue color, it is 
ready for use ; otherwise a fresh supply must be prepared. 



36 COMPOSITION AND MANUFACTURE OF FOODS 



Foods Tested in Which a Re- 
ducing Sugar Was Present 



Foods Tested in Which a Re- 
ducing Sugar Was Absent 



EXERCISE 9 

How can the presence of proteins in foods be shown? Laboratory 
demonstration. 

Put a small amount of white of egg (or casein of milk) in a test tube 
and add enough diluted nitric acid to cover the food substance. 
Bring the mixture to a boil. 

1. State the preparation of the experiment and give your observa- 
tion as to the color change in the protein. 

Note (to be studied). Nitric acid has the same color effect on all 
the proteins that it had on the one used in 1 above. No other class 
of food substances is affected in color by nitric acid as are proteins. 

2. Write out the method you would use in testing a given food for 
proteins. 

3. Test six or more common foods (for example, milk, flour, beans, 
parsnips, white meat of chicken, onions) and record your results in a 
table like the following : 



Foods Tested in Which Protein 
Was Present 



Foods Tested in Which Protein 
Was Absent 



EXERCISE 10 

How can the presence of fats in foods be shown? Home experi- 
ment. 

Put a small amount of some fatty substance (for example, butter, 
lard, or olive oil) on a piece of paper and hold the paper up to the light. 



COMPOSITION OF FOODS 



37 



Tell what you have done and describe the effect of the fat on the 
paper. 

Note (to be studied). Fats and oils are the only food substances 
that affect paper as did the fat in the experiment just performed. 
The spots are translucent, that is, the}' allow light to pass through 
more readily than does the rest of the paper. If the fat is combined 
with other food substances as in milk or corn meal, or if the percentage 
of fat is small, it is necessary to heat the substance to be tested on paper 
in an oven or over a hot radiator in order to melt the fat and drive 
off the water. 

2. Write out a method you would follow in testing a given food for 
fats or oil. 

3. Test six or more common foods (for example, any meat, one or 
more nuts, white and yolk of a hard-boiled egg, and wheat flour). 
Record your results in a table like the following : 



Foods Tested in Which Fat 
Was Present 



Foods Tested in Which Fat 
Was Absent 



Chemical Composition of the Food Substances 

How food analysis may be carried still farther. By 

separation methods in Exercises 5 and 6 and by special tests 
in Exercises 7 to 10 we have discovered that many of our 
common foods are composed of two or more simpler foods. 
These simpler foods we have called food substances. 1 Of 
course food substances are also foods, but each one contains 
only one kind, while the complex foods, like meat and 
potatoes, contain a number of kinds of food. The food sub- 
stances are the simplest forms of matter which we can use 
directly as food. 

1 These food substances are also known as foodstuffs and as nutrients. 



38 COMPOSITION AND MANUFACTURE OF FOODS 

Now are food substances composed of only one kind of 
matter or is each one a combination of simpler forms of 
matter? Before we begin the analysis (i.e. tearing apart) 
of each of the food substances, it will be necessary for us to 
become acquainted with the simplest forms of matter that 
enter into chemical combinations. These simple forms of 
matter are known as chemical elements. About ninety chemi- 
cal elements have been discovered, but we shall limit our- 
selves for the present to a study of some of those found in 
food substances. They are as follows : Carbon, oxygen, 
hydrogen, nitrogen, sulphur, and phosphorus. 

EXERCISE 11 
What are the characteristics of carbon? Home experiment. 

1. Prepare some charcoal by lighting a long splinter of wood or a 
match and then blowing out the flame. (Prepared charcoal may be 
used.) Charcoal is nearly pure carbon. 

a. Is carbon (charcoal) a solid, or a liquid, or a gas? What is the 

color of this form of carbon? 

b. Of what chemical element does this experiment prove that wood 

is partly composed? 

2. Hold the tip of the carbon (charcoal) in a hot flame for several 
minutes. 

a. Does any of the carbon disappear? 

b. Will carbon burn? How do you know? 

3. State three characteristics of carbon (charcoal) that you have 
learned from these experiments. 

EXERCISE 12 

What are the characteristics of oxygen? Laboratory demonstra- 
tion. 

Preparation of oxygen. Thoroughly mix a teaspoonful of potassium 
chlorate with about one fourth as much black oxid of manganese. 
Put the mixture in a large test tube. Close the mouth of the test 
tube with a stopper through which passes a delivery tube, the other end 



COMPOSITION OF FOODS 



39 



of which runs beneath the surface of water in a tray (111. below). Sup- 
port the test tube in a slanting position on an apparatus stand and 
heat the mixture with a gas or an alcohol flame until the oxygen 
begins to be given off. Fill 
three or four bottles with 
water, cover each with a 
piece of glass or cardboard, 
and invert the first one over 
the mouth of the delivery 
tube, removing the cover 
when the mouth is under 
water. Continue to heat 
the mixture until the bottle 
is full of oxygen, then cover 
it under water with the 




K 



Apparatus for the preparation of oxygen 

What is driving the water out of the bottle in the 

center of the picture ? 






glass plate or cardboard, and stand it right side up on the table. In 
the same way fill as many bottles with oxygen as are needed for the 
experiments. 

Prepare several bottles of oxygen as directed and allow them to 
stand until all fumes have settled, before answering the following 
questions. 

1. Examine a bottle of oxygen. 

a. Do you find oxygen to be a solid, a liquid, or a gas? 

b. State whether or not oxygen has color. 

2. Heat some charcoal (carbon) till it glows and thrust it into a 
bottle of oxygen. 

a. Tell what was done and describe what happens. 

b. Does carbon burn better in air (which is a mixture of oxygen and 

other gases) or in pure oxygen? 

3. State the three characteristics of oxygen which you have learned. 

EXERCISE 13 

What are the characteristics of hydrogen ? Laboratory demonstra- 
tion. 

Preparation of hydrogen (see Caution below) : Into a flask put 
some pieces of zinc. (111. p. 40.) Insert a stopper with two holes. 
Through one of the holes pass the lower end of a thistle tube until 
it nearly touches the bottom of the flask, and through the other run 



40 COMPOSITION AND MANUFACTURE OF FOODS 



a short piece of bent glass tubing. To the upper end of the latter 
attach a piece of rubber tubing long enough to reach beneath the 
surface of a tray of water such as that used 
in collecting oxygen. Pour through the thistle 
tube enough diluted hydrochloric acid to cover 
the lower end of the thistle tube. (If hydro- 
gen does not come off rapidly enough, put 
into the flask a bit of copper sulphate.) 
After the hydrogen has been given off for 
several minutes, collect a bottle over water 
in the same manner as in the oxygen experi- 
ment. Remove the bottle, holding it upside 
down, and place it on the desk in this posi- 
tion. Allow the bottle to stand until fumes 
disappear. 

1. Examine a bottle of hydrogen, and state 
whether hydrogen is a solid, a liquid, or a gas. 
Compare its color with that of oxygen and 
carbon. 

2. Thrust a lighted stick up into the mouth 
of an inverted bottle of hydrogen. (This ex- 
periment will be more satisfactory if the room 
is darkened.) 

a. State what was done and tell how the 
hydrogen affected the burning stick. 

b. How does the burning stick affect the hydrogen? 

c. What is one difference between oxygen and hydrogen? 

If hydrogen is not being given off from the delivery tube in sufficient 
quantity, pour into the thistle tube some more hydrochloric acid. 
Detach the rubber tube of the hydrogen apparatus and by means of 
a short piece of rubber tube or a rubber stopper insert in its place a 
piece of glass tubing, the upper end of which is drawn out to a small 
diameter. Caution. Make sure that all connections are tight so that they 
will not leak, since a mixture of hydrogen and oxygen, when lighted, 
will cause an explosion. After the hydrogen has been given off for 
several minutes, collect some of it by inverting a test tube over the 
small end of the delivery tube. Now bring the mouth of the inverted 
tube near the flame of a Bunsen burner or an alcohol lamp. If an 
explosion occurs, collect and light another tube of hydrogen. When 




Apparatus for preparing 

hydrogen 
Does the hydrogen come 
from the zinc or from the 
hydrochloric acid ? 



COMPOSITION OF FOODS 



41 



the hydrogen burns quietly at the mouth of the test tube, apply the 
burning gas to the end of the small delivery tube (111. p. 40). 

3. What happens to the hydrogen at the small end of the delivery 
tube when the flame is brought near it? 

4. Hold the mouth of an inverted, dry, cold glass tumbler or small 
jar over the burning hydrogen. What substance forms inside the glass ? 

5. What is the substance in air that causes the hydrogen to burn? 

6. What does this experiment show as to the composition of water? 

7. Name five characteristics of hydrogen. 



EXERCISE 14 

What are the characteristics of nitrogen? 

stration. 



Laboratory demon- 






Fasten a candle to a piece of cardboard and float the latter on a 
tray of limewater. Light the candle, and cover the flame with an 
inverted wide-mouthed 
bottle, bringing the lat- 
ter slowly down until the 
edge rests on the bottom 
of the tray (See 111.). 
Allow the candle to burn 
as long as it will. Then 
turn the bottle right side 
up, covering the mouth 
with the cardboard, 
keeping inside the bottle 
the limewater that has 
risen to take the place 
of the oxygen. Shake 
the contents of the bot- 
tle, to permit the lime- 
water to absorb the car- 
bon dioxid, and allow it 
to stand till the gas in 
the upper part of the jar is clear. Keep the bottle covered to prevent 
the mixing of outside air with the nitrogen in the bottle. 

1. Examine a bottle of nitrogen. Is nitrogen a solid, a liquid, or a 
gas? What is its color? 




Apparatus for the preparation of nitrogen 

How long will the candle continue to burn in the 

bottle of air ? 



42 COMPOSITION AND MANUFACTURE OF FOODS 

2. Thrust a burning splinter of wood into the nitrogen. 

a. Does the wood continue to burn? 

b. Does the nitrogen burn? 

c. In what respect does nitrogen differ from oxygen? From hy- 
drogen ? 

3. State four characteristics of nitrogen. 



-i --Oxygen 



Hydrogen -~ 



EXERCISE 15 

Is water a simple substance, or is it composed of two or more sub- 
stances? Laboratory demonstration. 

For this experiment an electrolysis apparatus similar to that shown 
on this page is necessary. (If such an apparatus is not available, this 

experiment may be omitted, and 
the problem of the composition 
of water may be worked out in 
connection with a review of Ex- 
ercise 13.) 

In order to induce an electric 
current to pass through water 
readily, add half a teaspoonful of 
sulphuric acid to a quart of water 
before pouring it into the central 
funnel of the electrolysis appara- 
tus. Open the two pet cocks at 
the top of the side tubes in order 
to fill each to the top with water. 
Attach the wires to a storage 
battery or to a light socket with 
a series of lights to cause resist- 
ance and allow the electric cur- 
rent to pass through the water. 

1. Draw or describe the elec- 
trolysis apparatus, and describe 
the preparation of the experi- 
ment. 

2. What evidence have you 
that water is being decom- 
posed ? 




Wires 
from 
battery 



Electrolysis apparatus for decomposing 
water 

What is the relative proportion of hydro- 
gen and oxygen? Why will there be no 
explosion when a lighted match is applied 
to the opened end of the tube containing 
hydrogen ? 



COMPOSITION OF FOODS 



43 



3. Are the substances forming at the top of the tubes liquids or 
gases? How do they resemble each other? 

4. Are the bubbles coming off equally fast in both tubes? How do 
you know? 

5. Determine in the following way whether the gases in the two 
tubes are the same or different : 

a. Apply a burning splinter to the gas formed in larger volume while 

it escapes as you cautiously open the pet cock at the top of the 
tube. Does this gas burn? Repeat the experiment several 
times until you are sure. What is the name of this gas? 

b. Hold a glowing splinter of wood or charcoal to the gas formed in 

smaller quantity in the other tube. Does it burn, or does it cause 
the splinter to burn more brightly ? Repeat the experiment until 
you are sure of your answer. What is the name of this gas ? 

c. What difference, therefore, do you find in the action of the two 

gases ? 

6. Of what two chemical elements, therefore, is water composed? 
What is the relative proportion of each ? 



EXERCISE 16 

Is cornstarch a simple sub- 
stance or is it composed of more 
than one chemical element? 

Laboratory demonstration. 

Warm some cornstarch in an 
old cooking spoon in order to 
drive off any water that may be 
in it, but do not allow it to burn. 
To determine when the starch is 
free from water, hold the heated 
starch under a dry, cold tumbler, 
and if no moisture collects upon 
the tumbler, the starch contains 
no water. Now set the starch on fire, and hold a cold, dry glass over 
the burning starch. 

1. Tell what was done and how you know that the starch is dry. 
State what is formed on the inside of the tumbler by the burning of the 
dry starch. 




Testing starch for hydrogen 
Why is the cold tumbler used ? 



44 COMPOSITION AND MANUFACTURE OF FOODS 

2. What is the only chemical element that could possibly form 
water by burning {i.e. by uniting with oxygen) ? 

3. What chemical element, therefore, must have been present in 
the cornstarch in order to have produced water when dry starch was 
burned? 

4. What substance is left in the cooking spoon after the flame goes 
out? 

5. Name two chemical elements that you have found present in 
cornstarch. 

6. State the final conclusion that is the answer to the problem. 

EXERCISE 17 

To partially determine the chemical composition of cane sugar, olive 
oil, white of egg. Laboratory demonstration. 

1. Test cane sugar in the same way as directed in Laboratory 
Exercise 16. Describe each of the experiments, and give the results 
and conclusions. 

2. In a similar way test olive oil. State what you did, what you 
saw, and what you concluded. 

3. Partially burn a piece of white of egg. Describe the experiment, 
and state your result and your conclusions as to one element present 
in white of egg. 

The chemical composition of the food substances. Water 
is one of the simplest of the food substances in its composition 
since it consists of only two chemical elements — hydrogen 
and oxygen, united in the proportion of two parts of hydro- 
gen to one part of oxygen. 

The carbohydrates include the starches and the sugars. 
These are composed of the three elements : carbon, hydro- 
gen, and oxygen. In starches and sugars the hydrogen 
and oxygen are always in the same proportion in which 
they are found in water (that is, twice as much hydrogen as 
oxygen). The name " carbohydrate," therefore, describes 
the composition of these substances, for carbo- signifies car- 
bon, and hydrate is derived from the Greek, meaning water. 



COMPOSITION OF FOODS 45 

Scientists find it more convenient to represent each of 
the chemical elements by a symbol, usually the capital 
letter with which the name of the element begins. Thus 
the symbol for carbon is C, for hydrogen H, for oxygen 0, 
and for nitrogen N. In grape sugar there are six parts of 
carbon, twelve parts of hydrogen, and six parts of oxygen. 
Hence the formula for grape sugar is CeH^Oe. It should 
be borne in mind, however, that no carbohydrate is simply 
a mixture of carbon with water ; instead, all the elements 
are closely united to each other. 

Fats too are composed of carbon, hydrogen, and oxygen but 
not in the same proportion as in carbohydrates. For this 
reason they are put in a separate class of food substances. 

Proteins are by far the most complicated and varied in 
their composition of all the food substances. Not only 
do they contain carbon, hydrogen, oxygen, and nitrogen ; 
but also another element, sulphur (S), a yellow solid in its 
elemental form, is usually present, and sometimes other 
elements as well. 1 

It is impossible to give any general statement as to the 
composition of the various kinds of mineral matter since no 
two of them are alike. Many of them, however, are white 
crystalline or powdery solids. Common salt (NaCl), for 
instance, or sodium chloride, as the chemists call it, is com- 
posed of two elements, sodium and chlorine. Sodium 
nitrate (NaN0 3 ) is made up of three elements — sodium, 
nitrogen, and oxygen. Whenever the name of the com- 
pound ends with ate or ite, we may be sure that oxygen is 
present. In calcium sulphate (CaS0 4 ) we find three ele- 
ments, calcium, sulphur, and oxygen. 

1 The following formula will give some idea of the extreme complexity of the 
composition of a protein that is found in the blood (as compared with the relatively 
simple composition of a carbohydrate) : C720H1134O248N21SS5. 



46 COMPOSITION AND MANUFACTURE OF FOODS 

Some Scientific Terms Used in Discussing Food 
Substances 

How elements, compounds, and mixtures differ. Carbon, 
oxygen, hydrogen, sulphur, and phosphorus are chemical 
elements. A chemical element is one of the simplest substances 
that can enter into combination. On the other hand, water is 
composed of two parts of hydrogen and one part of oxygen. 
From the fact that this substance consists of two elements 
that have been chemically united (by which we mean com- 
bined in such a way as to form a substance different from 
either one), it is known as a chemical compound. A chemical 
compound is a substance composed of two or more chemical 
elements united in definite proportion. One might naturally 
think that milk and flour are chemical compounds, since 
each is composed of more than one kind of substance. But 
since the various compounds found in them are not united 
in definite proportions, milk and flour are known as mixtures. 

What is meant by oxidation. Oxidation is the chemical 
union of oxygen with some other substance. It may take place 
slowly, as when carbon is made to glow in the air, or it may 
take place rapidly, as when carbon burns in oxygen. But 
whenever oxidation takes place, (1) an oxid is formed (for 
example, hydrogen oxid [water] is formed when hydrogen 
is oxidized), (2) a certain amount of heat is liberated, and 
(3) light is seen if the process is sufficiently rapid. 

What is meant by matter. We find that the world about 
us is made up of countless objects that we can touch, see, 
taste, or smell. Each of these objects has length, breadth, 
and thickness ; in other words, they all occupy space. Any 
substance that occupies space is known as matter. We have 
discussed carbon, hydrogen, oxygen, nitrogen, sulphur, 
water, starch, sugar, fats, proteins, and certain mineral 



COMPOSITION OF FOODS 47 

matters. All of these are forms of matter since they all 
occupy space. When we come to make a further study of 
matter, we find that it has another characteristic besides 
that of occupying space. All matter, under conditions with 
which we are familiar, has weight. 

What the three forms of matter are. In speaking of the 
different forms of matter, we have said that substances like 
oxygen, hydrogen, and nitrogen are gases. Matter like flour, 
sugar, starch and proteins, carbon and sulphur are solids, and 
substances like water are liquids. If the molecules (mol'e- 
kulz), that is, the smallest particles of which a substance is 
composed, move so freely upon each other that they tend to 
move out in every direction, we say the substance is a gas. 
If, however, the molecules of the substance have so little free- 
dom of movement that the shape of the matter is retained 
without using anything to hold it in, it is called a solid. If 
the substance tends to move outside laterally but not up- 
ward, it is a liquid. 

QUESTIONS AND APPLICATIONS 

1. Describe (a) each of the two kinds of substances you found in flour 
in Ex. 5, and (6) each of the four kinds you found in milk in Ex. 6. 

2. What did Ex. 5 and 6 teach you concerning the composition of these 
two foods? 

3. Name the class of food substance not found in Ex. 5 or 6. 

4. Name the class of food substance to which each of the substances 
found in flour and milk belongs. 

5. How can you determine whether or not each of the following sub- 
stances is present in a given food : (a) starches, (6) reducing sugars, 
(c) proteins, (d) water, (e) mineral matters ? 

6. What did you learn about carbon from your experiments with 
charcoal ? 

7. Name four food substances in which you found carbon. 

8. Can you find out whether carbon is present in water by the method 
used in Ex. 11? Give your reason. 



48 COMPOSITION AND MANUFACTURE OF FOODS 

9. State three characteristics of oxygen that you learned in Ex. 12. 
How does oxygen differ from carbon ? 

10. State five characteristics of hydrogen that you learned from the 
experiment in Ex. 13. 

11. State four characteristics of nitrogen learned in Ex. 14. 

12. How does nitrogen differ from oxygen ? From hydrogen ? 

13. How did you learn the composition of water? 

14. In what food substances did you find hydrogen? 

15. Why is it necessary to prove that a food substance is dry before 
attempting to demonstrate the presence or absence of hydrogen ? 

16. Name the food substances that contain only carbon, hydrogen, and 
oxygen. 

17. What chemical elements are always present in proteins? Name 
additional elements that may be present in proteins. 

18. What chemical elements are present in each of the following min- 
erals : sodium chloride, sodium nitrate, calcium sulphate ? 

19. How do compounds differ from both chemical elements and mix- 
tures? Name several compounds. 

20. Why are milk and flour mixtures rather than compounds? 

21. State two characteristics of all matter. 

22. Name three forms or states of matter, and give examples of each. 

23. What is meant by oxidation? What kind of compounds will 
always be formed during oxidation and what is it that will always be 
released during this process ? 

24. How could you tell whether or not gases of unknown composition 
in a closed bottle included a high percentage of (a) oxygen, (b) hydro- 
gen? 

25. Since cane sugar and cornstarch each contains carbon, why are 
these substances not black? 

26. How could you tell whether a brown liquid contained the element 
iodine ? 

PROBLEM 2. HOW ARE FOODS MANUFACTURED AND 
ASSIMILATED BY PLANTS? 

Food substances that exist ready-made, and those that 
must be manufactured by plants. All our common foods, 
whether derived from plants or animals, contain both water 
and mineral matter. Since these two classes of compounds 



FOOD MANUFACTURE IN PLANTS 49 

found in our foods are also found either in the air or in the 
soil, it is evident that both water and mineral matter exist 
ready-made for our use. 

We have found that starches, sugars, fats, and proteins are 
food substances derived from plants or animals. Do these 
food substances likewise exist ready-made in the air, water, 
or soil, or must they be manufactured by living things? 
We can account for their presence in animals because animals 
feed upon plants or upon other animals that secure their foods 
from plants. Plants, therefore, must somehow make the 
starches, sugars, fats, and proteins used by animals, by man, 
and by plants themselves since no one has ever discovered 
a supply of these substances in soil, water, or air. 

Some of the conditions necessary for carbohydrate manu- 
facture. All of us know that familiar plants have green 
leaves and that during a part of the twenty-four hours the 
leaves are exposed to sunlight. The green color of leaves is 
due to a green coloring matter known as chlorophyll (klo'- 
ro-fil, from the Greek, meaning the " green of leaves "). We 
shall now proceed to determine by experiments whether 
sunlight and chlorophyll are essential for carbohydrate 
manufacture. 

EXERCISE 18 

Is sunlight essential for starch manufacture in geranium (or hy- 
drangea) leaves? Laboratory demonstration. 

Select a vigorous green plant (e.g. geranium or hydrangea). Cover 
some of the leaves loosely with black carbon paper in such a way as 
to exclude all sunlight but to permit free circulation of air. Put the 
plant in direct sunlight in a warm room, or out of doors if the weather 
is favorable, and leave it for at least forty-eight hours. Now remove 
a leaf that has been exposed to sunlight several hours and also one 
that has been covered forty-eight hours. Break off the stem of the 
leaf that was deprived of sunlight so as to distinguish it from the one 
exposed to sunlight. 



50 COMPOSITION AND MANUFACTURE OF FOODS 



Boil the two leaves in water for a few moments in an agate or other 
available dish so as to soften the leaves. Remove the leaves from the 

water and put them into a flask 
with enough alcohol to cover 
them. Boil the alcohol over a 
piece of wire gauze or asbestos 
until all the green matter has 
been removed from the leaves. 
Rinse the leaves in water and 
test them in a saucer or Petri 
dish for starch. (Care must be 
taken, of course, to prevent the 
alcohol fumes from catching fire. 
It might be well to insert in the 
mouth of the flask a stopper, 
through which passes a glass tube 
at least six inches long.) (See 111.) 

1. Describe the experiment as 
performed. 

2. Give your observations 
after the leaves are tested for 
starch and state your conclusion 
about each leaf. 

3. State whether or not the 
Apparatus for removing chlorophyll leaves of a geranium plant must 

What liquid is used in this experiment, and be exposed to sunlight in order 
why? to manufacture starch. 




EXERCISE 19 

Is chlorophyll in a silver-leaf geranium (or coleus) plant necessary 
for starch manufacture ? Laboratory demonstration. 

Secure a plant having leaves that are partly green with chlorophyll 
and partly colorless, for example, silver-leaf geranium or coleus (111. 
p. 51). Expose the plant to direct sunlight in a warm room or out of 
doors for several hours. Remove a leaf and test it as directed in 
Exercise 18. 

1. Describe the way the experiment is performed. 



FOOD MANUFACTURE IN PLANTS 



51 



2. What is your observation, and what is your conclusion as to the 
presence of starch in the green and in the colorless portions? 

3. State whether chlorophyll is or is not necessary for starch manu- 
facture in the leaves of a silver-leaf geranium (or coleus) plant. 



Regions 

with 

.chlorophyll 




z Regions ^ 

without 
chlorophyll 




Leaves with green and non-green portions 
Coleus leaf at the left, geranium leaf at the right. Which parts will turn blue when 

tested with iodine ? 

Sources of materials used by plants in making food sub- 
stances. We have learned that plants are surrounded by 
soil, water, and air. Evidently a plant must obtain all the 
materials it uses from these sources. In other words, soil, 
water, and air must contain the substances that ultimately 
furnish all the substances needed by plants. Let us there- 
fore investigate these sources, and learn what each contains. 

Extent of our environment of air. Air is one of the most 
immediate parts of our environment. Not only does it 
surround our bodies and penetrate our clothing, but it also 
fills spaces between the particles of soil ; it is dissolved in 
water, for we can sometimes see the bubbles of air collecting 



52 COMPOSITION AND MANUFACTURE OF FOODS 



Vacuum — - 



on the inner side of a glass of water that has been allowed to 
stand for a time. Air extends outward from the earth's 
surface to a distance of perhaps two hundred miles. 

At sea level the air is dense enough to press upon every 
square inch of surface with a weight equal to about fifteen 
pounds. Scientists have shown that this 
pressure of the air can support a column 
of water thirty feet high or of mercury 
thirty inches high (See 111.) in a pipe 
that is closed at the top, provided the air 
inside the tube has been removed and 
a vacuum has thereby been formed. 

If we leave sea level and go up on a 
mountain top, or if we ascend in a bal- 
loon or an airplane, the height of the 
air above us becomes less and less, and 
consequently its weight and pressure be- 
come less than fifteen pounds per square 
inch. At a height of several miles the 
atmosphere becomes so rarefied, that is, 
so very thin, that aviators find it neces- 
sary to carry oxygen to breathe when 
r~>£~ l__^Zf) they ascend to higher levels. A device 
9 Mjft. WJ has been invented by which the airplane 
^551^ engine also may be supplied with oxy- 
gen in order to ascend still higher. 

The two principal gases found in air. 
In ancient times air was thought to be 
Indeed, some of the Greek philosophers 
universe was made up of four simple 
" principles," or substances: earth, air, fire, and water. 
Early in the seventeenth century, however, it was ascer- 
tained, as we have proved (Exercise 14), that the gas 



Torricellian tube 

What does this experiment 
demonstrate ? 

a single substance, 
believed that the 



FOOD MANUFACTURE IN PLANTS 



53 



which remained in an inclosed space where something had 
been burned (for example, a candle) could not support 
burning. The gas now known as nitrogen was then called 
" destroyed air," and the original air containing oxygen 
was spoken of as " fire air." It was not, however, until 
the second half of the 
eighteenth century, just 
before the American 
Revolution, that the true 
nature of the two prin- 
cipal gases in air was re- 
vealed by the celebrated 
French chemist, Antoine 
Lavoisier (la'vwa/zya') 
(See 111.). By a long 
series of experiments he 
proved that about one 
fifth of the air consists of 
a gas, oxygen, which sup- 
ports burning and that 
four fifths is made up of 
another gas, nitrogen, 
which does not support 
burning. 

Other substances found in air. Another substance found 
in air is water vapor. Ordinarily this is invisible, like oxygen 
and nitrogen. When the temperature of the air drops 
sufficiently, however, the vapor condenses in tiny droplets 
to form fog, and further condensation brings down the 
moisture in drops of rain. If the temperature drops still 
lower, flakes of snow are formed. That water vapor is 
present even on a clear day can often be proved by looking at 
the outside surface of an ice pitcher, for we find it covered 




Antoine Laurent Lavoisier (1743-1794) 

French chemist who showed the presence of 

oxygen in the air. 



54 COMPOSITION AND MANUFACTURE OF FOODS 

with beads of moisture. These drops do not come from the 
water within the pitcher, as many people think. Instead, 
they are formed on the cold surface by the cooling and 
condensation of the invisible moisture of the surrounding 
atmosphere. 1 

In addition to oxygen, nitrogen, and water vapor, air 
contains still another very important substance but in rela- 
tively minute quantities. This substance is carbon dioxid. 
Having already learned some of the characteristics of oxygen, 
nitrogen, and water, let us see what we can learn about 
carbon dioxid. 

EXERCISE 20 

What are the characteristics of carbon dioxid? Laboratory 
demonstration. 

Preparation of carbon dioxid: Into a flask put some pieces of marble, 
and insert a stopper through which passes a thistle tube and a delivery 
tube like that used in the preparation of oxygen. Pour into the thistle 
tube diluted hydrochloric acid until the lower end of this tube is 
covered. Collect a bottle of carbon dioxid in the same way that 
oxygen is collected, keeping the mouth of the bottle closed with a glass 
plate or cardboard (111. p. 39). Prepare a bottle of carbon dioxid as 
directed, and allow it to stand till all fumes have disappeared, before 
answering the following questions. 

1. Examine a bottle of carbon dioxid and state whether it is a solid, 
a liquid, or a gas. Compare this gas with oxygen as to its visibility. 

2. Light a splinter of wood and thrust it into the bottle of carbon 
dioxid. 

a. Describe the effect of the carbon dioxid upon the burning splinter. 

b. Did the carbon dioxid burn? 

3. Generate some carbon dioxid as suggested above and pass it 
through the delivery tube into a test tube of clear limewater. Tell 

1 The presence of moisture in air may be shown even better by the use of a highly 
polished metal container used in determining the dew point. The advantage of 
using the highly polished metal surface is that one can see the slightest deposit of 
moisture. 



FOOD MANUFACTURE IN PLANTS 55 

what was done and describe the effect of carbon dioxid on limewater. 
(Carbon dioxid is the only gas that affects limewater in this way ; 
hence limewater is a reliable testing substance for carbon dioxid.) 

4. State four characteristics of carbon dioxid and its effect upon 
clear limewater. 

EXERCISE 21 

How may the presence of carbon dioxid in air be shown? Lab- 
oratory demonstration. 

By means of a bicycle pump for at least five minutes force air 
through clear limewater that partly fills a tall bottle. 

1 . Describe the experiment, state the result, and give your conclusion. 

2. Do you infer from this experiment that the percentage of carbon 
dioxid in the air is large or small ? Give a reason for your answer. 

EXERCISE 22 

To show that carbon dioxid is formed only of carbon and oxygen. 

Laboratory demonstration. 

In order to answer this question it is necessary to secure a bottle of 
pure oxygen by the method described in Exercise 12. When bottles 
of oxygen have been obtained, proceed as follows : Hold some charcoal 
(which is nearly pure carbon) in a flame until it glows ; move the 
cardboard aside sufficiently to thrust the glowing carbon into the 
bottle of oxygen. 

1. Tell what is done w T ith the glowing carbon and describe what 
happens. 

2. After burning a piece of carbon in the bottle of oxygen, remove 
the cover sufficiently to pour in a small amount of limewater and cover 
again. Shake the bottle to mix the gas with the limewater. Describe 
the experiment, and state your observation and conclusion. 

3. Of what two substances must this gas now present in the bottle 
have been formed? 

4. What is one way, therefore, in which the gas carbon dioxid may 
be made? 

Some of the sources of carbon dioxid found in the air. If 
one were to hold a white porcelain plate in a candle or gas 



56 COMPOSITION AND MANUFACTURE OF FOODS 

flame, a black substance would collect on the plate. This 
substance is known as carbon. Similarly, when wood is 
partially burned, charcoal is obtained, which is composed 
likewise almost wholly of carbon. The black particles in the 
smoke that arises from any burning substance (for example, 
kerosene, soft and hard coal, sugar, starch, oil, and protein) 
is another evidence that carbon is a very common and, as we 
shall see later, a most important substance. 

We have already experimented with the burning of the 
carbon in Exercise 22. Now whenever any material con- 
taining carbon is burned, that is, when it unites with the 
oxygen in the air, carbon dioxid must be formed, just as it 
was formed when the carbon was burned in the bottle of 
oxygen. 

Another source of the carbon dioxid in the air becomes 
apparent when one breathes through a glass tube into a 
bottle or test tube partly filled with limewater. 1 The milky 
appearance of the limewater produced by a single breath 
shows that a human being must form and give off a con- 
siderable quantity of carbon dioxid in the course of twenty- 
four hours. Similar experiments with other kinds of living 
things show that they likewise form and give off carbon 
dioxid as long as they are alive. 

Some of the uses that man makes of carbon dioxid. 
Possibly you may think that the first time you ever saw 
carbon dioxid was when we generated it in Exercise 20 by 
pouring hydrochloric acid on marble. However, you have 
probably seen carbon dioxid many times, without realizing 
it. This is the gas which is used in charging beverages like 
ginger ale, sarsaparilla, vichy water, soda water, and many 
others. Let some ginger ale or any carbonated beverage 
stand in a glass for a moment before drinking. What do 

1 This experiment should be demonstrated by the teacher (see Exercise 47). 



FOOD MANUFACTURE IN PLANTS 



57 



— 1-^^- s —Ac/cf 



So/ut/on 
' of Soc//um 
H/cerbonate 



you see rising rapidly to the surface of the liquid? This 
effect is due to the carbon dioxid which is escaping in the 
form of bubbles. Let the gas escape as long as it will. Now 
taste the ginger ale. Do you like the taste as well as before ? 
Can you now see why soft drinks 
are usually charged with carbon 
dioxid ? 

Water highly charged with 
carbon dioxid is also used in 
certain types of fire extinguishers 
(See 111.). What characteristic 
of carbon dioxid learned in your 
study in Exercise 20 would make 
it useful in this kind of fire ap- 
paratus? 

Extent of our environment of 
water. Geographers tell us that 
three quarters of the surface of 
our globe is covered by the 
waters of oceans, lakes, ponds, 
rivers, brooks, and the like. In 
the oceans the water is some- 
times found to be more than 
five miles deep. Indeed it is 
estimated that, if the surface 

of the earth were level and if all the waters were to be 
evenly distributed over the globe, the covering of water 
would everywhere be a mile deep. The atmosphere absorbs 
and holds considerable quantities of water vapor. Particles 
of soil, too, even if apparently dry, are usually covered with 
a film of moisture, and beneath the surface of the earth are 
countless underground reservoirs of water. Later we shall 
find that the bodies of all living things — plants, animals, 




Section of a fire extinguisher 

What gas is produced in this appara- 
tus when it is inverted ? 




58 COMPOSITION AND MANUFACTURE OF FOODS 

and man — consist to a large extent of this extremely com- 
mon substance. 

In what forms water may exist. Water at ordinary 
temperatures is a liquid ; under other conditions it may be 
an invisible gas or a solid. If one looks at a rapidly boiling 
teakettle, an apparently empty space extending about half 
an inch from the mouth of the spout is seen (111. at left). 
That this space is really filled with invisible water vapor can 

be readily shown by placing a cold 
steam^ plate close to the nozzle. The 

plate immediately becomes wet. 
This is due to the fact that the 
water vapor has become condensed 
by the cold surface. When the 
temperature of water is reduced to 
A teakettle of boiling water 32° Fahrenheit (or 0° centigrade), 

Is gaseous steam visible or not? the Uquid solidifieg and expandS) 

forming solid ice, which is somewhat lighter in weight than 
a corresponding volume of water and floats at the surface. 
(See 111. p. 59.) 

What some of the characteristics of soil are. Anyone 
who has worked on a farm or in a garden knows that soil 
is made up of particles of varying degrees of coarseness. In 
ordinary soil the coarse sol d masses are known as gravel. 
If these particles are much smaller, they are called sand. 
Clay particles are exceedingly minute. If we have a mixed 
sample containing all these components, they may be sepa- 
rated into layers in the following way : Mix thoroughly 
in a tall jar of water a cupful of the soil to be tested and 
allow the mixture to stand until the water has become clear 
once more. We shall then find that the coarser parts, gravel, 
have settled on the bottom of the jar, the sand above them, 
and after some time the clay forms a layer above the others 



FOOD MANUFACTURE IN PLANTS 



59 



(111. p. 60). All these components of soil are purely of 
mineral origin. They are produced by the disintegration, 
or breaking down, of various kinds of rocks through the 
action of water, snow, ice, and wind. 

Plants obtain most of the mineral foods they need from 
the clay and almost none from the sand, which is largely 




Photograph by Swing Galloway 



A floating iceberg 

The bulk of floating ice below the surface is about eight times as great as that above 
the surface of the water. Compare the size of the iceberg (probably a half mile distant) 
with the size of the Eskimo in his kayak. 

made up of grains of a very hard glassy substance known as 
quartz. Sand, however, is a useful part of the soil, since 
it makes the ground loose, porous, and easy to cultivate. 
When leaves, straw, roots, or other plant materials decay or 
when animal wastes (manure) are added to the soil, they 
give to the earth the substances that are stored up in these 



60 COMPOSITION AND MANUFACTURE OF FOODS 



< 



compounds, much of which was originally taken from the 
soil. This decayed animal and vegetable matter is known 
as humus. This is the dark-colored top soil, which is loose 
and easily penetrated by air, water, and the roots of plants 

(111. p. 310). Loam is a mixture of 
clay with sand or gravel and humus 
and is the most productive kind of 
soil. 

Distributed in the finer particles 
of rich soil, especially near the sur- 
face, are important chemical com- 
pounds, which we shall find are used 
by growing plants. Among these 
necessary compounds are sodium 
nitrate (Chili saltpeter), potassium 
nitrate (saltpeter), sulphate of lime 
(gypsum), phosphate of lime, and 
iron chloride (111. p. 61). 1 

The compounds used by plants 
in making carbohydrates. We have 
learned that carbohydrates, fats, and 
proteins are all compounds ; that 
starches, sugars, and fats contain 
only carbon, hydrogen, and oxygen ; 
and that proteins have nitrogen in 
addition to these three elements, and usually sulphur and 
sometimes other elements as well. One might suppose that 
the plant could use the oxygen of the air in making carbo- 
hydrates and fats and both the oxygen and the nitrogen in 
making proteins. It has been demonstrated, however, that 

1 The teacher should demonstrate the experiment described above, and should 
show samples of various kinds of soil and the chemical compounds mentioned 
together with any others that are useful to plants. For the living components of the 
soil, see pages 374-376. 




ffumus — 
C/ay- — 
Sand- — 
Grave /- 



Experiment with soil 
Note that the gravel settles 
first and the humus last. Give 
reason. 



FOOD MANUFACTURE IN PLANTS 



01 



living organisms cannot manufacture food from chemical 
elements. Instead, simple compounds containing these ele- 
ments must be available. 

From what compound, then, in soil or air is derived the 
hydrogen which is always present in carbohydrates? Thus 



I 



POTASSIUM 
NITRATE 










( f "1 > 


1 




I ~^\ 


SULPHATE 

OF 

LIME 


WSSM 




X 


/ 


w 


1 


f \ 


IRON 


CHLORIDE 


^\^W 


Y^lft 


w*Kj 


£31 




%1m 







Chemical compounds found in the soil 
What use do plants make of each of these compounds ? 

far we have mentioned the following compounds as being 
present in air or soil : 

Carbon dioxid (C0 2 ) Iron chloride (FeCl 2 ) 

Water (H 2 0) Sodium nitrate (NaN0 3 ) 

Calcium sulphate (CaS0 4 ) Potassium nitrate (KN0 3 ) 
Calcium phosphate (Ca 3 (P0 4 )2) 

Evidently water is the only one of these compounds that 
contains hydrogen, and this will help us to remember that 
the hydrogen for carbohydrate manufacture is all derived 
from this source. It is probable that the needed oxygen is 
also obtained from water, especially since in all the carbo- 
hydrates the hydrogen and the oxygen are always in the 
same proportion as in water (H 2 0). 



62 COMPOSITION AND MANUFACTURE OF FOODS 

From what compound does a plant obtain its necessary 
supply of carbon? Going over the list of compounds in 
the preceding paragraph, we find that carbon is present in 
carbon dioxid only. Hence it would seem that this com- 
pound must be the source of the needed carbon. 

EXERCISE 23 

Do green plants give off a gas in sunlight, and not in darkness? 

Laboratory demonstration. 

Into each of two tall glass cylinders put some fresh water that has 
been poured from one jar into the other several times, in order to secure 
a plentiful supply of carbon dioxid, and several sprays of Elodea 
(e-lo'de-d), milfoil (111. p. 63), or other plant that grows beneath the 
water, fastening the plants at the bottom of the jars by means of a 
weight if necessary. Put one of the cylinders in direct sunlight and 
cover the other with a lightproof box, keeping the temperature the 
same in both cases. 

1. Describe the preparation of the experiment. 

2. Examine the jar that has been in sunlight ; then quickly raise the 
box and look at the other jar. State your observations in both cases. 

3. What is your conclusion from the experiment with the plant that 
you have used ? 

The gas that green plants give off only in sunlight. The 

following method may be used to determine the kind of gas 
given off when green plants manufacture carbohydrates. 1 
A large glass jar or an aquarium is filled with water that has 
been well mixed with air by repeated pouring back and forth. 
In the jar a large glass funnel is completely submerged (111. 

1 This experiment is extremely difficult to perform successfully since bubbles of 
air from the outside of the plant are sure to mingle with the oxygen that comes from 
the inside of the plant. It is also difficult to keep the plant in the direct sunlight 
long enough to get sufficient oxygen to make the test. Again, if the preparation is 
left overnight, the plant gives off carbon dioxid (instead of oxygen), which mingles 
with the gases in the test tube and so neutralizes the effect of the oxygen. The 
student should know, however, that extremely delicate experiments have been 
performed which show that the gas given off from green plants in sunlight is oxygen. 






FOOD MANUFACTURE IN PLANTS 



63 



below), and beneath the larger end of the funnel is placed 
a handful of water plant (Elodea or milfoil). Over the 
smaller end of the funnel is inverted a test tube filled with 
water. (Be sure that the mouth of the test tube is under 
water.) When the ap- 



Oxygen 
gas 




paratus is put in strong 
sunlight, bubbles of gas 
rise from the water plant 
through the funnel and 
gradually force the water 
out of the test tube. 
After the test tube is 
filled with the gas, the 
funnel is removed from 
the test tube under the 
water, and the mouth of 
the tube is covered with 
the thumb. On remov- 
ing the test tube and 
thrusting into it a glow- 
ing piece of carbon, we 
find that the carbon 
either bursts into a flame 
or glows more brightly 
than in air. This proves 
that the gas given off in 
the presence of sunlight 
is oxygen, since there is 
more oxygen present than in ordinary air. It has been found 
that the oxygen obtained in this way corresponds exactly 
to the amount supplied by the carbon dioxid. 

The manufacture of carbohydrates by green plants. The 
necessary compounds for carbohydrate manufacture (i.e. 



A-Bubbles 

of 

oxygen 



Green 
water 
plant 



Aquarium plants in sunlight 
What gas is bubbling up through the water ? 



64 COMPOSITION AND MANUFACTURE OF FOODS 

carbon dioxid and water) must be supplied to the leaves or 
other green parts of a plant. Then sunlight must act upon 
the chlorophyll. Through the action of the sunlight the 
chlorophyll bodies combine the chemical elements (carbon, 
hydrogen, and oxygen) found in carbon dioxid and water, 
thus forming a carbohydrate (111. p. 65). The excess of oxy- 
gen is given off from the leaves as we have seen in Exercise 
23. Sugar is made before starch, and the sugar is changed 
to starch only when more sugar is formed than the plant needs 
for its immediate use. It is easier to prove the presence of 
starch than of sugar in leaves, and for this reason we have 
used the starch test to show that carbohydrate manufacture 
is going on. To this process of carbohydrate manufacture 
is given the name photosynthesis (fo'to-sm'the-sis, from the 
Greek, meaning putting together by light). 

The manufacture of fats and proteins by plants. Sugar 
is doubtless the foundation of all food substances. Fats, as 
we have already shown, contain the same three chemical 
elements (C, H, and O) that are found in sugars and starches 
but in different proportions. It is probable, therefore, that 
fats are made in plants by transforming the sugar. 

Proteins are far more complex than either carbohydrates 
or fats since they contain nitrogen and in most cases sulphur 
and sometimes phosphorus and other elements in addition 
to carbon, hydrogen, and oxygen. The carbon, hydrogen, 
and oxygen in proteins are furnished by the sugar already 
formed in the leaves. The nitrogen, sulphur, and phos- 
phorus (if present) are obtained from the nitrates, sulphates, 
and phosphates carried up through the plant in the soil water. 
In the manufacture of proteins neither sunlight nor chloro- 
phyll is essential ; hence, these food substances may be 
formed in any part of a plant and at any time, provided sugar, 
nitrates, and sulphates are present. A moderate degree of 



FOOD MANUFACTURE IN PLANTS 



65 



warmth, however, is essential for the making of proteins and 
for carbohydrate and fat production as well. 

The manufacture of protoplasm by plants. In order to 
make protoplasm, the plant, animal, or man must have 
proteins, water, and additional compounds containing iron, 
calcium, and several other chemical elements. These must 



Protop/asm 




Assimilation 



Storage 



Photosynthesis 



Additional Additional Mineral Carbon Water 

Water Miner a/ matter dioxide f/f^ &) 

matter ( co ^J 



Diagram of food manufacture, storage, and assimilation 

be supplied from the environment or, in the case of protein, 
be manufactured by plants. But so far as we now know, 
only protoplasm has the power to combine these compounds 
in such a way as to form living matter. 

Bearing in mind the facts we learned in food manufacture, 
we see that a plant begins with simple compounds (carbon 
dioxid and water) and manufactures a more complex sub- 
stance (sugar). It uses this sugar and other substances 
(nitrates, sulphates, phosphates, and possibly other com- 



66 COMPOSITION AND MANUFACTURE OF FOODS 



pounds) to make a still more complex substance, protein. 
Finally, by using protein, water, and mineral compounds 
containing phosphorus, iron, calcium, and several other 
elements, it ends by making the most complex substance of 
all, protoplasm (111. p. 65). But all plants must have com- 
pounds to start with ; they cannot make any of these food 

subst ances or protoplasm 
directly from chemical 
elements. 

Thus we learn that 
food materials are grad- 
ually changed by proto- 
plasm into living sub- 
stance like itself. To 
this process is given the 
name assimilation, which 
denotes the change of 
foods to living matter, or 
protoplasm. 

How the leaves of 
plants are adapted for 
photosynthesis. If you 
were asked what parts of 
plants are best fitted for 
carbohydrate manufacture, it seems quite certain that you 
would say: " The leaves." And if you were asked for a 
reason for your answer, doubtless you would state something 
like the following : " Leaves are the parts of plants that 
have most of the green coloring matter in them, and also 
offer the largest exposure to sunlight." The only plants of 
which this would not be true are those plants that have no 
true leaves, such as the cacti (111. p. 67). In these plants the 
stems have been modified so that they can do the work of 




Courtesy of Brooklyn Botanic Garden 

Leaf exposure to light 
Note that the leaves are so arranged as not to 
shade one another. What is the advantage to 
the plant of such an arrangement of leaves ? 



FOOD MANUFACTURE IN PLANTS 



67 



leaves. But even in these cases the stems have most of the 

chlorophyll in them and offer the greatest amount of surface 

exposure to the sun. 

In this connection it 

is interesting to note 

that leafy plants 

often have their 

leaves arranged so as 

not to shade one an- 

other. (See 111. 

p. 66.) 

But this is not all. 
Have you never won- 
dered how the chlo- 
rophyll bodies are 
arranged in the leaf ? 
You have learned 
that leaves, like all 
parts of plants, are 
composed of count- 
less numbers of cells. 
If you were to ex- 
amine a cross-section 
of a leaf by the aid 
of a compound mi- 
croscope, you would 
see that the inside of 
the leaf is made of 
cells each of which 
has many chlorophyll 
bodies arranged close to the cell walls (111. p. 68). Observe 
that the cells in the upper and lower layers (except the guard 
cells) have no chlorophyll. These are the cells of the epi- 




A giant cactus 
What part of the cactus manufactures carbohydrates ? 



68 COMPOSITION AND MANUFACTURE OF FOODS 



dermis or skin. The cells of the onion that you studied in 
Exercise 3 were taken from the epidermis of the onion. 

Let us now peel off some of the lower epidermis of a leaf in 
the way shown on page 69 and examine it by the aid of the 
compound microscope. In the illustration on page 151 you 

will see many cells 



Upper 
epidermis cells — - 



Palisade 



Chlorophylls 
bodies -- >. 
(green) 



Air spaces <-'- 

Lower 
epidermis cells - — Jc^ 




not unlike those of 
onion skin, but 
among these are 
some cells quite dif- 
ferent in shape and 
arranged in pairs. 
Part of the inner 
surface of each of 
these cells is hol- 
lowed out so that 
the two cells do not 
meet in the center 
but leave a tiny 
opening between 
the two cells. Each 
opening is called a 
stoma (sto'md), 
plural stomata (sto'- 
md-td) . Now what 
are these openings 
for ? Stoma comes from a Greek word which means literally 
a mouth. The two cells on either side of the stoma are known 
as guard cells. In the illustration on this page you will see 
that each stoma opens into a space inside the leaf surrounded 
by cells, containing chlorophyll bodies. These spaces are 
called air spaces. Now what will be the use of the stoma 
and air chambers? Of course you will say the spaces will 



Stoma with a guard 
cell on either side 

Section of leaf 



QC 



Where are chlorophyll bodies found and where are 
they absent? What cells cannot manufacture carbo- 
hydrates ? Where does carbon dioxid enter the leaf ? 



FOOD MANUFACTURE IN PLANTS 



69 



hold air and the air will come in through the stoma. Right, 
but what will be in the air that can be used by the cells con- 
taining chlorophyll? We hope you said " Carbon dioxid," 
for that is what comes in through the stoma into the air 
spaces, to be used in making carbohydrates in the chloro- 
phyll-bearing cells. Another use for the millions of stomata 
is to permit the escape of water and of excess 
of oxygen that is released from the carbon 
dioxid during photosynthesis (111. p. 63). 

How the roots of plants are adapted to help 
furnish water and mineral for food manu- 
facture. You have doubtless observed how 
plants in the garden will wilt or droop on hot, 
dry days after a long dry spell. Suppose you 
pour water on the ground around the plant 
and watch the plant. Will not the leaves and 
young stems very gradually begin to straighten 
up and finally become rigid again? Is it not 
evident that the soil water must have passed 
into the roots, and up the stems to the leaves, 
thus reviving the plant? How, then, are 
roots fitted to absorb soil water? This will 
be evident to j^ou if you will examine the roots of seedlings 
grown on moist blotting paper (111. p. 70). You will see 
projecting from these roots countless numbers of tiny deli- 
cate hairlike bodies known as root hairs. Each root hair 
is a projection from one of the outer cells of the root 
(111. pp. 141 and 146). Root hairs are splendidly adapted 
for absorbing soil water (water containing minerals) because 
(1) they have very thin walls, (2) they extend out into the 
soil and so expose much surface to the soil, and (3) there 
are countless numbers of them on the young parts of all 
growing roots. 




Courtesy of Brooklyn 
Botanic Garden 

Live-forever 

leaf 

Epidermis being 

peeled off. 



70 COMPOSITION AND MANUFACTURE OF FOODS 



Why food manufacture in green plants is important. This 
process of food manufacture in plants that contain chloro- 
phyll is the foundation of all the food supply of the world, 
since all plant foods are dependent upon the formation of 

carbohydrates. Ani- 
mals are unable to 
make any of the food 
substances out of 
carbon dioxid, water, 
and mineral matter 
as do green plants. 
They can only trans- 
form in their own 
bodies the carbohy- 
drates, fats, and pro- 
teins secured from 
plants or from other 
animals. 

Moreover, other 
important sub- 
stances in plants are 
also made from car- 
bohydrates, such as 
the cell walls (cellu- 
lose) and all the 
wood. In fact, there 
is nothing manufactured in a plant that does not depend 
upon the carbohydrates, since, as we have said, these are 
the first compounds made. Again during photosynthesis 
green plants use much more carbon dioxid than they form 
and give off much more oxygen than they use, thus making 
the air more suitable for breathing, for plants, animals, and 
man. 




Courtesy of Brooklyn Botanic Garden 

Mustard seeds sprouting on moist blotting paper 

What are the projections on the roots and what is their 

function ? 



FOOD MANUFACTURE IN PLANTS 71 



QUESTIONS AND APPLICATIONS 

1. Name the classes of food substances that do not have to be manu- 
factured by plants and give the reason for your answer. What are the 
other classes of food substances ? 

2. How do you know that each of these must be manufactured ? 

3. What is chlorophyll and in what parts of the plant is it most com- 
monly present? 

4. To what are the leaves of a plant exposed during, at least, part of 
the twenty-four hours ? 

5. In the experiment to determine whether a plant must be exposed 
to sunlight to manufacture starch — (a) Why were some of the leaves 
covered with carbon paper? (b) Why is it necessary to remove the 
chlorophyll from these leaves before testing with iodine? (c) Give your 
observations and immediate conclusions after adding iodine to the leaf 
exposed to direct sunlight several hours and to the leaf covered forty-eight 
hours, (d) State your final conclusions. 

6. In the experiment to determine whether chlorophyll is necessary 
for starch manufacture — (a) Give your observations and immediate 
conclusions after testing the leaf partly green and partly colorless. 
(b) State your final conclusion. 

7. What are the original sources from which must come all the raw 
materials used by plants in making food substances ? 

8. Of what two substances is air largely composed? Are these sub- 
stances elements or compounds ? 

9. How did we prove the presence of carbon dioxid in air? Is the 
percentage large or small ? How could you tell ? 

10. How did you prove that carbon dioxid is composed only of oxygen 
and carbon? 

11. What are some of the living and non-living sources of the carbon 
dioxid in the air? 

12. Where on the earth is water visibly present? Is water found in 
air and in soil ? How do you know ? 

13. Name five mineral compounds found in rich soil and give the 
chemical elements in each. 

14. What is the name of the best kind of soil and what does it 
contain ? 

15. What is humus and why is it so important as a soil constit- 
uent? 



72 COMPOSITION AND MANUFACTURE OF FOODS 

16. What is the only compound in soil, air, or water that you know of 
that could furnish the carbon found in carbohydrates ? What must be the 
source of the hydrogen needed in food manufacture ? 

17. What compound is the probable source of the oxygen in carbo- 
hydrates ? Why ? 

18. What is photosynthesis ? What materials and what conditions are 
essential for this process in plants ? 

19. What gas is given off from green plants in the sunlight ? How can 
this be demonstrated? 

20. What food substance is used as a basis for making starch, fats, 
and proteins? 

21. What additional substances from soil must be used in making 
proteins ? 

22. State two of the ways in which leaves are usually better fitted for 
photosynthesis than other parts of a plant. 

23. What are stomata and air spaces, and how is each useful in photo- 
synthesis ? 

24. How are roots, root hairs, and stems useful in photosynthesis? 
In the manufacture of proteins and protoplasm? 

25. State the importance to all living things of food manufacture in 
green plants. 

26. What is assimilation, and what classes of food substances are 
necessary in this process ? 

27. Make a list of plants and parts of plants which cannot manu- 
facture carbohydrates, and tell why they are unable to do so in each case. 

28. Why would it be impossible to secure a good crop of potatoes if 
weeds were allowed to grow freely among the potato plants ? 

29. Find out why it is possible for mushrooms to grow to maturity 
in the dark. 

30. How may the chlorophyll stains in white garments be removed ? 



UNIT III. HOW FOODS ARE PREPARED FOR 
USE IN LIVING THINGS 

PROBLEM 1. HOW ARE FOODS PREPARED FOR 
DISTRIBUTION AND USE IN PLANTS? 

How we know that food materials are transported through 
plants. Vegetables like potatoes, beets, carrots, and onions 
grow beneath the ground. In testing these foods (Unit II, 
Problem 1), we found supplies of starch or sugar or both. 
These food materials can be manufactured only in the pres- 
ence of sunlight by cells that contain chlorophyll (Unit II, 
Problem 2). It should be evident, therefore, that manu- 
factured food materials in some form must travel from the 
leaves where they are manufactured to their place of storage 
beneath the ground. On the other hand, in order to manu- 
facture carbohydrates and proteins in the leaves, water and 
mineral matter must travel through the plant from the soil. 
Hence, food substances move upward and downward through 
the plant, and so must pass into cells and out from cells. 

Questions that might be asked with reference to the move- 
ments of food materials in plants. We have just seen that 
food materials must pass both into and out from the cells 
of plants. Would you think that the presence of cell walls 
and of protoplasm would help or hinder the passage of these 
food substances ? Do you think that food substances will be 
more likely to pass from cell to cell in a solid or in a liquid 
state ? Since some of these substances must sometimes move 
upward directly against the force of gravity, is there any 
form of energy we can discover that may act in such a way 

73 



74 PREPARATION OF FOODS FOR USE 

as to overcome gravity ? Do any substances with which you 
are familiar tend to intermingle when they are brought into 
contact ? To some of these puzzling questions we shall find 
answers in the text and the experiments that follow. 

What is meant by diffusion of gases? If a gas like 
ammonia is set free in one part of a closed room, in a short 
time the odor of the ammonia will be detected in all parts of 
the room even if there are no currents of air. This means 
that the ammonia has become distributed throughout the 
room. Every one who has had any experience with ordinary 
illuminating gas knows how quickly this mixture of gases 
will spread through the air of a room. The process by which 
gases spontaneously intermingle is known as diffusion of 
gases. Now it should be noted that diffusion of gases is 
independent of the action of gravity ; for if carbon dioxid 
were set free at the bottom of a room, this heavy gas would 
still pass upward and intermingle with the lighter air. 

Some scientific terms needed in discussing diffusion of 
liquids. Suppose we place a spoonful of sugar in a glass of 
water and then stir the mixture. What becomes of the 
sugar? You will say that the sugar has dissolved. Now 
what happens when a solid like sugar is dissolved in water? 
Can you see the sugar in the water? " Of course not/' you 
will answer. Perhaps you might think that you could see 
the particles of sugar in a drop of the mixture if you were to 
examine it by the aid of a compound microscope. These 
particles of sugar, however, are now so extremely small that 
the highest powers of the microscope cannot reveal them. 
In fact, scientists believe that the sugar particles in solution 
are the smallest that can exist and still retain their identity. 
Such extremely small particles are called molecules. Hence, 
whenever a substance is truly dissolved, it is broken up into 
molecules and so becomes invisible unless, of course, it has 



FOOD DIGESTION IN PLANTS 75 

color. But even then the individual molecules cannot be 
seen. 

Now any substance that will dissolve in another substance 
is said to be soluble in that substance. Thus, for instance, 
sugar and salt are both soluble in water. Moreover, the 
matter (usually a liquid) which dissolves the substance is 
called a solvent. That is, water is a solvent of both sugar and 
salt and of so many other substances that it is sometimes 
called the universal solvent. The combination of the sub- 
stance dissolved and the solvent is known as a solution. So 
sugar and water form a solution. 

There are, however, some substances that seem to dissolve 
in another substance, but really do not, since their particles 
are large enough to be revealed either by a compound mi- 
croscope or by a special microscope known as the ultra- 
microscope. Such substances are white of egg, starch paste, 
and gelatin. They do not break up into molecules when 
water is added, and so do not form true solutions. 

On the other hand, we have other substances that do not 
even seem to dissolve in water, for one can see the particles 
in the water with the unaided eye. Thus if you place a 
teaspoonful of clean white sand in a tumbler of water, you 
can see the sand settling at the bottom. If the water is all 
poured off, after the sand has settled, and if the sand is 
dried and weighed, it will be found to have the same weight 
as the sand that was put in the water. Evidently none of 
the sand dissolved in water. Sand, therefore, is said to be 
insoluble in water. Phosphate of lime is also insoluble in 
water, while sulphate of lime is only slightly soluble, that 
is, only a very little will dissolve in each quart of water 
used. 

What is meant by diffusion of liquids ? In order to show 
that liquids diffuse we should first secure some red ink and a 



76 PREPARATION OF FOODS FOR USE 

glass of water. Fill a pipette with the ink and carefully 
force it out over the bottom of the glass containing the water. 
Without disturbing its contents, set the glass aside for several 
days. You will then observe that some of the red ink has 
moved upward through the water. In other words, it has 
diffused throughout the water, in spite of the fact that the 
ink is heavier than water. 

A similar experiment may be tried with molasses or with 
a dense solution of salt. In these cases complete diffusion 
takes place much more slowly than in the experiment with the 
red ink ; indeed it may require several weeks. After five or 
six days, however, if the liquid in the upper part of each 
glass is tested, it will be found to contain grape sugar or salt, 
as the case may be. Evidently, then, these substances which 
form true solutions in water, diffuse through the water. 

We learned that in true solutions the particles (molecules) 
of the dissolved substance are so finely divided in the solvent 
that no microscope has been devised that will reveal their 
presence. Salt and sugar probably break up in water into 
molecules of salt or sugar and then are diffused throughout 
the molecules of water. It is believed that this is what 
happens in all true solutions of solids in liquids. 

Will insoluble substances and substances that do not form 
true solutions in water diffuse in water? Place in a glass 
a tablespoonful of some mineral matter, such as phosphate 
of lime, that is practically insoluble in water, and add sev- 
eral tablespoonfuls of (distilled) water. While stirring this 
mixture, draw up in a large pipette as much as possible. 
Now gently plunge the end of the pipette to the bottom of 
another glass of distilled water and slowly force out the mix- 
ture of mineral matter and water on the bottom of the glass. 
Prepare in a similar manner two other glasses, but place in 
one a mixture of raw white of egg and water, and in the other 



FOOD DIGESTION IN PLANTS 77 

a mixture of starch paste and water. Cover the three glasses 
and allow them to stand for five days or more. 

If the water in the glass in which the phosphate of lime 
was placed is then examined, it will be seen that the mineral 
matter has settled on the bottom of the glass ; it shows no 
sign of having diffused through the water. The same will be 
found true of the starch paste and of the w T hite of egg. It 
will be noticed, however, that neither the mixture of white of 
egg nor that of the starch paste has settled appreciably. It 
occupies about the same space in the water that it did when 
first put on the bottom of the glass. If chemical tests are 
made of the water in the upper part of each of the glasses, no 
phosphate of lime, protein, or starch will be found. Evi- 
dently, then, the insoluble mineral matter and the apparently 
soluble white of egg and starch paste show no appreciable 
diffusion in water. 

How substances are classified as to diffusibility. The 
substances found in living things may be classified as follows : 
(1) gases like oxygen and carbon dioxid that diffuse readily in 
each other ; (2) solid substances like sugar and salt that dis- 
solve in water and then diffuse slowly ; (3) solid substances, 
such as starch and certain proteins, in a very finely divided 
condition, that seem to form solutions in water, but really do 
not, and that show little or no tendency to diffuse in water ; 
and (4) solids like phosphate of lime that do not dissolve nor 
appear to dissolve, and which do not diffuse at all in water. 
We may now raise the questions which of these substances 
will be able to pass into and out from cells and which will not. 

Under what conditions must diffusion occur in living 
things ? Before taking up experiments to show what is true 
with reference to diffusion into and out from cells, it is neces- 
sary to consider the various conditions under which inter- 
change of food substances must take place. First, it must 



78 



PREPARATION OF FOODS FOR USE 



Cell wall 

Protoplasmic 

membrane 



be evident that the substances inside the cells and outside 
the cells will not be in immediate contact with each other, 
as were the various substances used in our previous diffusion 

experiments. Between dead 
plant cells there will usually 
intervene a cell wall of cel- 
lulose, and in living plant 
cells there is an additional 
membrane made up of a 
layer of protoplasm next to 
the cell wall (111. at left) . In 
living animal cells there will 
be at least a membrane com- 
posed of an outside layer of 
protoplasm, and in addition 
there may be another mem- 
brane (cell wall) made by 
the protoplasm. Hence, in 
order to enter or leave living 
cells, it is evident that food 
materials must pass through 
some kind of membrane. 
Let us first try an experi- 
ment with cells in which there is no protoplasm but only a 
dead membrane made up of the walls of animal cells. Now 
will a solvent (water) and a true solution of a substance dis- 
solved in water pass, or diffuse, through such a membrane ? 




Cell sap 



Cytoplasm if- 



Cell nucleus 



A plant cell 
Which parts are alive and which are lif eless ? 



EXERCISE 24 

Will water or sugar dissolved in water pass through a membrane ? 

Laboratory demonstration. 

Materials: a thistle tube, a beaker or bottle ; honey, molasses, or 
a thick solution of grape sugar or other reducing sugar; Benedict's 



FOOD DIGESTION IN PLANTS 



79 






CrflkcKl 



-Sugar 
solution 



solution or Fehling's solution. Procure the intestines of a calf or of 
beef, wash them thoroughly inside and out, and blow them up by 
inserting a large glass tube. Tie at intervals of about two feet, and 
allow this membrane to dry. Cut off pieces about two inches long, 
and slit open each of the pieces thus obtained. Membranes thus 
obtained may be kept for years in a 
closed jar. Sausage coverings that 
have been preserved in salt also may be 
used after they have been thoroughly 
washed and dried. The lifeless mem- 
branes we have described are composed 
of cell walls only. 

Hold the thistle tube upright, clos- 
ing the smaller end by pressing on it 
with the thumb or with a piece of rub- 
ber tubing closed with a clamp. Into 
the larger end of the thistle tube pour 
the honey, molasses, or reducing sugar 
that has been warmed sufficiently to 
pour easily. Half-fill the tube and 
nearly fill the bulb. Moisten one of 
the pieces of membrane, and fasten it 
tightly over the bulb of the thistle tube 
by means of elastic bands or a thread 
so that none of the liquid can escape. 
Wash off any of the liquid from the 
outside of the membrane ; then dry 
with a blotter. Hold the thistle tube 
upside down long enough to make 
sure that the sugar solution does not 
leak out. 

Support the thistle tube, the membrane being down, in a beaker of 
water, in a slanting position or suspended by a ring-stand (111. above). 
Mark on the thistle tube with an elastic band the level of the sugar 
solution, and set the experiment aside for fifteen minutes or until the 
next day. If the experiment is to continue for several days, connect 
a long piece of glass tubing to the smaller end of the thistle tube by 
means of a short rubber tube and support the long glass tube in a 
vertical position. 




— Water 



^Membrane 



Osmosis experiment with water 
and sugar 
How can you tell that water is 
passing through the membrane 
more rapidly than the sugar? 



80 PREPARATION OF FOODS FOR USE 

1. Describe the preparation of the experiment. Make a labeled 
drawing of the apparatus. 

2. State whether or not there is any change in the level of the grape- 
sugar solution within the thistle tube. Has the water passed through 
the membrane or not? How do you know? 

3. Test the liquid in the beaker for a reducing sugar. Tell what was 
done, and state the result. How do you account for the result? 

4. What substances have you proved will pass through a membrane 
composed of cell walls ? 

5. Which of the two substances passed through the membrane the 
more readily: the water (solvent) or the dissolved sugar? How do 
you know? 

Some definitions and explanations. We have seen in the 
experiment just tried that both water and grape sugar in 
solution diffuse through a membrane and thus mingle with 
each other. Diffusion of gases or liquids through a membrane 
is osmosis (5s-mo'sis). 

We have proved that water passed through the membrane 
much more rapidly than did sugar, and this is likewise true 
in the case of salt and nitrate of potash and other soluble 
minerals dissolved in water. Hence we see that solvents 
pass through the membranes more freely than do dissolved 
substances. Some membranes, however, as we shall see 
later, prevent the passage of dissolved substances but permit 
the free passage of the solvent. 

Now the fact that the molecules of the dissolved substance 
(sugar in Exercise 24) could not diffuse out as rapidly as the 
molecules of water diffused in, caused the solution in the 
thistle tube to rise. If the membrane does not give way on 
account of the weight of the column of liquid, the mixture will 
finally cease to rise in the thistle tube. This result may be 
due to either one of two causes. If the membrane permits 
the passage of dissolved substances, but less freely than the 
solvent (as was the case of the membrane in Exercise 24), 



FOOD DIGESTION IN PLANTS 



81 



the dissolved substance (sugar) will pass through the mem- 
brane into the water until the percentage of sugar on both 
sides of the membrane will be the same. When the percent- 
age of sugar is the same on both sides of the membrane, the 
percentage of water on both sides of the membrane will also 
be equal. Therefore the movement of sugar and water in 
and out will thereafter continue to be equal ; hence the liquid 
would cease to rise in the thistle tube. 

If, on the other hand, the membrane is of such a nature as 
to permit the passage of the solvent only, the dissolved sub- 
stance (sugar) cannot diffuse through the membrane at all 
and the solvent (water) will pass inward till the downward 
pressure of the molecules of liquid on the membrane is equal 
to the pressure of the molecules of water tending to pass up- 
ward and inward. In this case the liquid will rise much 
higher than it would where the membrane simply interferes 
with the passage of the dissolved substance. Even with a 
membrane like that used in Exercise 24 it is possible to cause 
a rise of liquid in a suit- 
able tube to a height of 
from six to ten feet. 
You will therefore see 
how osmosis and water 
pressure may help to 
explain the rise of water 
in the roots and stems 
of plants. 

Let us now consider 
the effect of having the 
dissolved substance inclosed so there will be no opportunity 
for the liquid to rise. This may be done in an experiment like 
the following. Carefully remove the shell at the large end of 
a hen's egg in such a way as to leave the membrane cover- 




CSurface of__) 
water 

Egg 

membrane 



Support - 

of egg 




At the beginning 
of the experiment 



About one hour 
later 



Osmosis experiment with an egg 

What caused the change in shape of the egg after 

an hour ? 



82 



PREPARATION OF FOODS FOR USE 



Cell wall 



ing the contents of the egg unbroken. Support the egg at 
the bottom of a beaker or drinking glass (111. p. 81) and 
cover the egg with rain water or distilled water. (If ordinary 
drinking water is used, a very small percentage of soluble 
mineral matter may be present.) Over half of the contents 
of the egg is water, but there is a much higher percentage of 
dissolved substances in the contents of the egg than in drink- 
ing water, if that is used. Hence, in either case, the greater 
percentage of water will be on the outside. Since the greater 
flow of solvent (water) is always toward the point of lesser 
percentage of solvent, and the movement of the solvent is 
always greater than that of the dissolved substance, we have 
a condition favorable for the osmosis of water inward. The 
dissolved substances, being more con- 
centrated in the egg than in the water, 
will tend to pass outward, but will either 
be hindered or prevented from so doing 
by the egg membranes. The result after 
several hours is shown on page 81. 
The water pressure within the egg will 
finally be so great that the membrane at 
the open end of the egg will be broken. 
Now in the case of the egg we have 
been dealing with one large cavity in- 
closed by non-living membranes, which 
only interfere with the passage of dis- 
solved substances. Let us now see what 
will happen where we make use of a liv- 
ing part of a plant, such as that of a common potato, and have 
the conditions the same as in the egg experiment. The 
potato consists of an enormous number of cells (See 111.), 
each surrounded by a non-living membrane (cell wall) and 
also by a living membrane, that is, a thin layer of proto- 



Starch 
grains 




Cell sap 



Protoplasmic membrane 

Osmosis experiment with 
living cells of potato 
Which part of these cells 
contains soluble food sub- 
stances? Which part has 
a selective action during 
osmosis ? 



FOOD DIGESTION IN PLANTS 83 

plasm close to the inner surface of a cell wall. In each cell 
there will be soluble substances such as sugar, mineral 
matter, water, and also insoluble matter such as starch and 
protein. Bearing these facts in mind, let us proceed with 
the following experiment. 

EXERCISE 25 

To show osmosis and water pressure in living potato cells. Home 
experiment. 

Peel a portion of a potato. Cut several cross sections of the peeled 
part of the potato, each about an eighth of an inch in thickness. 
Allow these sections to stand in the air until they have wilted on 
account of the loss of water by evaporation. Now place some of the 
wilted sections in a glass half filled with clear cool water and set aside 
for a half hour or more. 

1. Describe the way the experiment is performed. 

2. Remove from the water one of the sections of the potato and 
bend it between the fingers. How does it compare in stiffness with the 
section before it was placed in water? 

3. Was the greater percentage of water in the cells of the potato 
or outside of the cells, when they were first placed in the water? From 
what you have learned, would you expect the water to pass in greater 
quantity into the cells or out from the cells ? What makes you think 
the movement you have mentioned has actually occurred in this slice 
of potato you have just tested? 

4. State whether or not the water passed through both the cell 
walls and the protoplasmic membranes of these potato cells. 

5. What process must have gone on in the potato sections in 
water ? 

6. How is water pressure shown in this experiment ? 

How osmosis and water pressure are useful to plants. 

Much of the interchange of soluble materials and solvents 
between cells in both plants and animals is due to osmosis. 
This process quite largely accounts for the absorption of soil 
water by the roots of plants. Doubtless it partly accounts 



84 PREPARATION OF FOODS FOR USE 

for the upward movement of sap through the roots, stems, 
and leaves. 

But in plants, at least, water pressure serves other useful 
purposes. You observed in the experiment with the potato 
sections (Exercise 25) how the inward flow of the water filled 
out the cells so that the whole section was rigid or turgid. 
This is the way that the stems and leaves of herbaceous plants 
are kept rigid and erect. Every one has noted that wilted 
plants or cut flowers are revived and that celery stalks are 
stiffened when they are supplied with water. If the cells of 
herbaceous plants are not kept rigid with water, the plant 
wilts and finally dies. When the plant is well supplied 
with water, the water pressure within the cells is so great 
that the cells are thereby stretched, and the cells are made 
larger. 

One might expect that this stretching process would cause 
the cell walls to break. This does sometimes occur, but 
usually the cells keep the walls intact by gradually adding 
more cellulose (the material of which cell walls are made) as 
the walls are stretched and therefore become thinner. The 
growth of plants, therefore, is also dependent on osmosis and 
water pressure. Without this pressure in young cells the 
walls would soon become so rigid that further enlargement 
would be impossible. 

Do insoluble substances or substances that do not form 
true solutions pass through membranes? On page 76 
we have shown that insoluble substances like phosphate of 
lime and insoluble starch do not diffuse appreciably in water. 
Neither does white of egg, in spite of the fact that it is appar- 
ently (though not really) soluble in water. Now the question 
arises — Is it likely that these substances will diffuse through 
membranes? The following experiment will help us to 
answer this question. 



FOOD DIGESTION IN PLANTS 85 

EXERCISE 2G 

Will starch pass through a membrane ? Laboratory demonstration. 

Set up a thistle tube as in Exercise 24, except that a starch-and-water 
mixture is used in the thistle tube in place of the sugar solution. 
Allow the experiment to stand over night at least. 

1. Describe the preparation of this experiment. 

2. How can you determine whether or not starch has passed through 
the membrane? 

3. Make the test ; record the result and your immediate conclusion. 

4. What is your final conclusion from this experiment? 

What food substances will diffuse through membranes 
and what will not ? Repeated experiments show that water 
and gases very readily diffuse through a membrane, and that 
sugar, common salt, and nitrate of soda in solution also pass 
through membranes, but much less freely. In the case of 
starch, fats, proteins, and insoluble minerals, other experi- 
ments prove that they will neither diffuse in water nor pass 
through membranes. 

Osmosis in living cells. In Exercises 24 and 26 we made 
use of lifeless membranes, but in the potato cells in Exercise 
25, as in all living cells of plants and animals, the living mem- 
brane formed by the protoplasm (111. p. 78) must be taken 
into account. It has been discovered that this protoplasm 
acts as a selective agency so that the passage of certain dis- 
solved substances may be prevented, while the solvent may 
diffuse freely in either direction. Thus the water on the out- 
side of the cell might enter the cell through the membranes 
rapidly, while the dissolved minerals or sugars inside might 
not pass outward at all, or at one time might pass through, 
and at another time might not. This is undoubtedly due to 
the conditions in the membrane of protoplasm. As condi- 
tions change within the protoplasm, the osmosis of dissolved 
substances and of solvents is found to vary. 



86 PREPARATION OF FOODS FOR USE 

However, an interchange, whether due to osmosis or not, 
must go on in each cell of a plant or of an animal, and it is the 
conditions in the protoplasm that apparently control the en- 
trance and the exit of the solvent water and of the various 
dissolved substances. We have already seen, however, that 
osmosis does not take place in the case of starch, and this is 
also true of proteins, fats, and of mineral matters that do 
not dissolve in water. None of these substances, therefore, 
can pass through the living membranes formed by proto- 
plasm. 

Why insoluble food substances must be changed before 
they can pass through membranes. Substances like water, 
sugar, and some mineral matters in solution can pass from 
cell to cell in the manner we have described. But the starch 
which we found stored in leaves and underground parts like 
potatoes is in the form of solid, insoluble grains that will not 
pass through cell membranes. Hence, before this insoluble 
starch can pass through the various membranes from the cells 
where it is stored to the cells where it is needed, it must be 
changed to a more soluble carbohydrate, namely, sugar. We 
shall now determine by experiment that this change in starch 
actually occurs. 

EXERCISE 27 

Does a growing seedling change its starch to sugar? Laboratory 
demonstration. 

Materials: Dry unsprouted and sprouted grains of corn (or barley 
or oats) that have been pulverized or mashed. 

1. Test the unsprouted grains for starch and for reducing sugar. 
Describe the method used, and state your observations and con- 
clusions. 

2. In a similar way test the sprouting grains for reducing sugar. 
What do you find, and what do you conclude as to the presence of this 
substance in the sprouting grains? 



FOOD DIGESTION IN PLANTS 



3. What change must have taken place in some of the starch in the 
grains? 

4. Of what advantage would the change, stated in the answer to 3, 
be to the corn, barley, or oat seedlings? 

What is meant by digestion and by digestive ferments, 
or enzymes? We have seen in the preceding experiment 
that insoluble starch in seeds is changed to soluble sugar 
during the process of 
sprouting. The change 
from an insoluble food 
substance to a soluble food 
substance is known as 
digestion. Substances 
have been found in plants 
that are able to trans- 
form insoluble foods into 
soluble foods, and these 
are known as digestive 
ferments or digestive en- 
zymes (en'zimz) . One of 
these digestive ferments 
is known as diastase 
(di'd-stas). 

EXERCISE 28 

Does diastase digest 
cooked starch ? Laboratory 
demonstration. 




Courtesy of Brooklyn Botanic Garden 

Sundew plant 
Note the sticky hairs (tentacles) on the margins 
of the leaves and the captured insects. The in- 
sects that alight on the leaves are caught by the 
tentacles which bend over the insect and pour 
out a protein-digesting enzyme. 



Boil some arrowroot 
starch (about half of the 
size of a pea) in half a test 
tube of water to make a very thin paste. Cool the mixture and 
divide it into two parts. Dissolve in half a test tube of water a very 
small amount of diastase. To a portion of the starch mixture add half 



88 PREPARATION OF FOODS FOR USE 

of the diastase and water, and set the mixture aside, shaking it occa- 
sionally. 

1. Test for a reducing sugar one half of the contents of the tube 
containing diastase and water alone. State the result and the con- 
clusion. 

2. Test the contents of the tube containing starch paste alone for 
a reducing sugar. State the result and the conclusion. 

3. After ten minutes test half of the contents of the tube containing 
starch paste and diastase for a reducing sugar. Compare the result 
with the result obtained by testing for sugar the contents of the tube 
containing diastase and water alone. What is the result and what is 
your conclusion as to the comparative percentage of reducing sugar in 
the two mixtures? 

4. What change has evidently taken place in some of the starch 
in the mixture of starch and diastase ? 

5. At the end of twenty minutes or on the following day test the rest 
of the starch and diastase mixture for starch. What is the result and 
what do you conclude? What, therefore, must have become of all 
of the starch? 

6. What is your conclusion as to the action of diastase on cooked 
starch? 

(This experiment may be performed successfully with raw starch 
if sufficient time is allowed for the action of the diastase.) 

How other food substances are digested. We have 
learned that proteins and fats resemble starch in that they 
will not pass through cell membranes. Hence, these sub- 
stances also, before they can pass, or diffuse, through mem- 
branes, must be digested. These changes in proteins and 
fats are brought about by protein- and fat-digesting enzymes. 
Each kind of enzyme digests only one kind of food substance, 
and each acts in a manner similar to that of diastase. All 
digestive ferments are made by protoplasm. 

Why foods must be digested within cells. Let us suppose 
that a cell is able to manufacture within itself all the starch, 
fat, and protein that it needs. This probably occurs in cells 



FOOD DIGESTION IN PLANTS 89 

that contain chlorophyll. The question then arises — 
Would the cell still need to digest these food substances? 
Biologists find that starch is always changed to grape sugar 
before it can be used in making protein or for any other pur- 
pose. Again, proteins cannot be used in making living 
substance until they have been acted upon by digestive 
ferments. And finally fats cannot be utilized until they, too, 
have been digested. In other words, not only does digestion 
prepare food substances for passing through cell membranes, 
but this process is also necessary before foods can be used 
for any purpose within the cell itself. Each cell, then, 
must be capable of producing within itself the enzymes 
necessary to digest the food substances that it uses. 

QUESTIONS AND APPLICATIONS 

1. In stucfying food manufacture what evidence have you (a) that 
water must travel from the soil through roots, stems, and into leaves, and 

(b) that carbohydrates in some form must travel from the leaves to the 
roots or underground stems ? 

2. Through what structures of a plant must substances travel in 
order to pass through a plant from roots to leaves? Or from leaves to 
roots ? 

3. Define the following terms : (a) solvent, (b) soluble substance, 

(c) solution, (d) diffusion of liquids. 

4. What evidence have you (a) that a drop of red ink and water will 
diffuse ? (6) That molasses and water will diffuse ? 

5. Will insoluble substances diffuse? How do you know? 

6. What structures in a living plant would seem likely to interfere 
with diffusion of dissolved substances and solvents? 

7. How did the thistle tube experiment demonstrate that the solvent 
water was passing through the dead membranes composed of animal cells? 

8. In the experiment just referred to, how was it proved that the 
reducing sugar in the molasses had also passed through the membrane? 

9. In Exercise 24 why was it necessary to test the membrane for leaks ? 
Why must the membrane be rinsed with water before being immersed in 
the bottle of water? 



90 PREPARATION OF FOODS FOR USE 

10. How does the thistle tube experiment in Exercise 24 show that the 
solvent diffused through the membrane more rapidly than the dissolved 
sugar ? 

11. Will solvents and dissolved substances move more freely toward 
the region of greater percentage of each substance or toward the region 
of lesser percentage ? 

12. If the mixture in the thistle tube is prevented from rising on account 
of the closing of the tube at the top, how will water pressure become 
evident? 

13. How did you show with potato sections that water diffused inward 
more rapidly than anything diffused outward ? 

14. How was water pressure shown in the potato sections in the water? 

15. What would happen to rigid sections of potato if they were placed 
in a solution of sugar and water such that the percentage of water would 
be greater inside the cells of the potato than outside? Give reason for 
your answer. (If in doubt, try the experiment and see what happens.) 

16. What are two uses of water pressure to plants? 

17. In the exercise with starch and water inside the bulbs of the thistle 
tube (instead of molasses and water) , how were you able to tell whether or 
not starch passed through the membrane? 

18. Why must insoluble food substances in plants be changed to sol- 
uble substances? 

19. (a) What is meant by digestion ? (b) What are digestive ferments ? 
(c) Name a digestive ferment found in plants. 

20. (a) What food substance did you prove to be present in the un- 
sprouted grain you used and what food substance was absent? (b) What 
food substance was present in sprouted grain that was not present in the 
unsprouted ? (c) What do these tests prove ? 

21 . (a) How could you tell that there was a greater percentage of reducing 
sugar in a mixture of diastase water and cooked starch than in another test 
tube containing the same amount of diastase as in the first but no starch ? 
(b) What did this experiment show ? (c) After the mixture of diastase and 
starch had stood for twenty minutes or overnight and iodine was added, 
what were your observation, immediate conclusion, and final conclusion? 

22. How are proteins digested ? How are fats digested ? 

23. Why must starches, proteins, and fats be digested even in the cells 
where they are made? 

24. What then are the two reasons why starches, fats, and proteins must 
be digested by plants? 



FOOD DIGESTION IN THE HUMAN BODY 91 

PROBLEM 2. HOW ARE FOODS PREPARED FOR DISTRI- 
BUTION AND USE IN THE HUMAN BODY? 

How we know food materials are transported through the 
bodies of human beings and of animals. In the human body 
every living cell of the muscles or of other tissues must have 
food for repair or growth and for various activities. The 
same is true of all forms of animal life with which we are 
familiar. Unlike green plants, our bodies and those of the 
animals we know cannot manufacture these foods, and so 
they must be taken in at the mouth. In order to reach the 
various cells of which we have spoken, these food substances 
must travel through all parts of the body. Moreover, when 
the various tissues are tested for food substances, we find all 
classes represented. Therefore, food substances in some 
form must pass into all the cells of the bodies of animals. 

It must be evident, therefore, that insoluble starches, 
fats, proteins, and mineral matter must be made soluble, 
i.e. digested, before they can diffuse through the cell mem- 
branes and thus reach the various cells of the human body. 
As in plants, digestion of insoluble food substances is also 
necessary in the human body and in animals in order that 
these substances may be used in the cells. 

Where digestion takes place in the human body. The 
carbohydrates, proteins, mineral matter, and most of the 
fats needed by our bodies to furnish material for repair or 
growth and for our various activities are supplied from the 
plant or animal foods that we eat. Our foods are taken into 
our bodies through the mouth opening and pass down 
through a rather complicated tube, the alimentary canal. 
So long as it remains within this tube, food is not available 
for use by the brain, muscles, or other organs of the body, for 
none of these food substances, with the possible exception of 



92 PREPARATION OF FOODS FOR USE 

some of the sugars and some of the minerals, is diffusible. 
Hence, they must be digested before they can pass through 
the cell membranes and enter the blood or any of the working 
tissues. We are now to study the organs of the body, known 
as the digestive organs, which are of two kinds, namely, the 
alimentary canal, in which the food substances are digested, 
and the digestive glands, which furnish the digestive juices 
containing enzymes. 

Parts of the alimentary canal. The alimentary or food 
canal (111. p. 93) consists of the following parts : mouth 
cavity, throat cavity, gullet, stomach, small intestine, and 
large intestine. Let us now consider these various regions 
more in detail. In reality the alimentary canal begins at 
the mouth opening, which leads into the mouth cavity. The 
mouth cavity narrows at the back considerably and thus 
communicates with the throat cavity (111. p. 94). Below the 
throat cavity the alimentary canal continues as a tube of 
rather small diameter, the gullet, which conducts the food 
downward through the neck region and through that part 
of the body containing the heart and lungs, called the chest 
cavity. After passing through a muscular partition known as 
the diaphragm, the gullet enters the lower cavity of the trunk, 
the abdomen (ab-do'men), or abdominal cavity. Here the 
food tube becomes greatly enlarged to form a pouch, the 
stomach, which in adults ordinarily holds about three pints. 
From the stomach the food is forced through a long, much- 
coiled tube about twenty feet in length called the small intes- 
tine, which occupies a large part of the abdominal cavity. 
Finally, what remains of the food we have eaten enters a some- 
what larger part of the tube, the large intestine, which com- 
municates through an opening with the exterior. Hence, it is 
evident that so long as the food remains in the alimentary 
canal, it is not in any real sense within the body, but is rather 



FOOD DIGESTION IN THE HUMAN BODY 93 



inclosed by a tube which extends from the mouth to the lower 
end of the trunk with no openings by which food might enter 
any other part of the body. But even if food substances 



Salivary glands 
Windpipe 



Gall -~^4 
bladder 

m 



Liver - 
(raised) 



Vermiform 
appendix 




--;/— Salivary 
gland 



Esophagus 
{gullet) 

— Stomach 
Pancreas 



— Large 

intestine 



-Small 
intestine 



Parts of the alimentary canal and the digestive glands 

could enter other parts of the body, they could not be used 

since only digested food substances can be used by the cells. 

Digestive glands and digestive juices. We know that, if 

non-diffusible foods are to be made diffusible and also ready 



Cranium^ 



Mouth 

Throat cavity 
Larynx -" 
Windpipe — 
Gullet - 

Breastbone — 
Lung — 

Heart — 



~~.'~ ™k — Cerebrum. 

— Cerebellum 
Medulla 



Thoracic cavity — 
Diaphragm — 
Abdominal cavity 
Liver •"*" 
Stomach— 
Large intestine 
Kidney — \ 

Small intestine' 

Ureter- 
Vermiform 
appendix"" 

Urinary bladder' 




„i. Lumbar 
vertebrae 
(5) 



Urethra 



K Anus 



Section of head and trunk 






Opening— 
from 
duct 

Duct - 

Glands- 
cavities 



FOOD DIGESTION IN THE HUMAN BODY 95 

for use, digestive ferments, or enzymes, are necessary. In 
our bodies these are supplied by special organs, the digestive 
glands, which consist of masses of special cells found either 
in the walls of the digestive tube or lying outside this tube. 
In either case the digestive juices containing the ferments 
formed in these gland cells enter the mouth cavity, the 
stomach, or the small intestine 
through longer or shorter pipes, 
called ducts (111. at right). 

The first digestive juice to act 
upon the food is the saliva. Saliva 
oozes out into the mouth from three 
pairs of salivary glands located in 
the walls of the mouth cavity (111. 
p. 93). When food is swallowed, 
it passes through the gullet into the 
stomach and is here mixed with 
gastric juice which comes from 
countless tiny gastric glands in the 
walls of the stomach. The open- 
ings of the ducts of the gastric 
glands are shown on page 104. Likewise, the walls of the 
small intestine contain innumerable intestinal glands which 
supply the small intestine with intestinal juice. 

Unlike the three kinds of glands just named, the two re- 
maining digestive glands are found outside the alimentary 
canal. The first of these is a large gland on the right side of 
the stomach. It is known as the liver and its secretion is 
called bile (111. p. 93). The liver, unlike the other digestive 
glands, has a special organ for holding any excess of its se- 
cretion called the gall bladder (111. pp. 106 and 117). Gall is 
a name applied especially to the bile of an ox. The second 
digestive gland found on the outside of the alimentary canal 




Capillary 
network 

Secreting cells 
Structure of a gland 
How are the necessary mate- 
rials for preparing its secretion 
brought to the gland ? 



96 PREPARATION OF FOODS FOR USE 

is called the pancreas (par) 'kre-as) , and its digestive secretion, 
pancreatic juice. The pancreas is located just behind the 
lower part of the stomach. The bile and the pancreatic 
juice enter the small intestine by a common duct ; that is, 
the ducts from the liver and pancreas unite before entering 
the small intestine (111. p. 93). Some of the ferments con- 
tained in these digestive juices digest starch as does diastase 
in plants ; others digest proteins ; and still others make fats 
ready for absorption. Let us now determine the digestive 
effect of one of these juices upon cooked starch. 

EXERCISE 29 
Does saliva digest cooked starch? Laboratory demonstration. 

Collect some saliva in a test tube by chewing on a piece of rubber. 
Prepare some thin arrowroot starch paste as in Exercise 28. Divide 
the mixture in halves and add some filtered saliva to one half and shake 
the mixture at short intervals. 

1. Test the starch paste and then the saliva for a reducing sugar. 
Is it present in either? How do you know? 

2. After five or more minutes test the contents of the tube contain- 
ing both starch and saliva for a reducing sugar. Tell what was done. 
State the result and the immediate conclusion. 

3. What is your conclusion as to the action of saliva on cooked 
starch ? 

Note (to be studied). In the saliva there is a digestive enzyme, 
called ptyalin (tl'd-lin), similar to diastase in its action on starch. 
Ptyalin has no digestive action on raw starch since it cannot digest 
the outer covering of cellulose. Boiling bursts open the cell walls and 
also the starch grains. 

EXERCISE 30 

What is the action of the cheeks and the tongue in chewing and in 
swallowing food? Home experiment. 

1. Press your forefinger against the roof of the mouth, the side walls 
outside the teeth (cheeks), and the floor of the mouth cavity. The 



FOOD DIGESTION IN THE HUMAN BODY 97 

walls that are rigid are composed largely of bone ; those that are yield- 
ing are made largely of muscle. Which walls are composed of bone and 
which are composed of muscle? Give reasons for your answers. 

2. To what part of the mouth cavity is the tongue attached? 
Which end of the tongue is free? 

3. While chewing a piece of solid food, observe and then explain how 
the tongue and cheeks act to keep food between the teeth. 



Brain cavity — # — 



Soft palate -. 
closing off 
nose cavity 



Food masses :" 




^Uard palate 

)% 

— Mouth opening 

Mouth cavity 
"" ^Tongue 



If/JSSI ' l^M^WtWSilf ^Epiglottis closing 
/I £31 ir^ffilr^M °ff wind-pipe 

' it 9 Gullet 

Section of head and neck 
Notice position of soft palate and of epiglottis during swallowing of food. What is 
accomplished by the position of each of these organs ? 

4. Repeat a number of times the act of swallowing some solid food. 
Note the action of the tip of the tongue and then explain how the 
tongue acts in forcing food into the throat (See 111.). 



EXERCISE 31 
A study of the teeth. Home experiment. 

Note (to be studied). There are two kinds of cutting, or biting, teeth, 
the incisors (from the Latin, meaning to cut into) and the cuspids (from 



98 



PREPARATION OF FOODS FOR USE 



Incisors 



the Latin, meaning one point). There are also two kinds of grinding 
teeth, the bicuspids (from the Latin, meaning two points) and the molars 

(from the Latin, meaning 
Cuspid Bicusptite Motors millstone) 1 (111. at left). 

Use a hand mirror to 
determine the number of 
teeth of each kind that 
you have, the number of 
cavities and fillings in 
each kind, and then 
record the numbers in a 
table in your notebook 
as follows : 




Kinds of teeth in permanent set 

What differences do you note in the crowns and in the 
roots of the four kinds of teeth ? 





Upper Jaw 


Lower Jaw 




RIGHT HALF 


LEFT HALF 


RIGHT HALF 


LEFT HALF 




A 
Teeth 


'umber c 

Cavi- 
ties 


>f 
Fill- 
ings 


A 

Teeth 


' umber ( 

Cavi- 
ties 


>/ 
Fill- 
ings 


A 
Teeth 


'umber ( 

Cavi- 
ties 


>/ 

Fill- 
ings 


A 
Teeth 


T umber c 

Cavi- 
ties 


>/ 
Fill- 
ings 






















































Bicuspids 













































































EXERCISE 32 

How are the teeth adapted for biting and chewing food? Home 
experiment. 

1. Bite off a piece of apple or bread and describe the action of the 
lower jaw in this process. 

2. In what part of each jaw are found the teeth that are used in 
biting off pieces of food ? 

3. Describe the cutting edge of one of the incisors and one of the 
cuspids. 

1 Human teeth may be obtained from a dentist. They should be cleaned by being 
boiled in strong caustic soda solution and then in water. If time permits, each 
student should examine and make a drawing of one of each of the kinds of teeth 
named above. 



FOOD DIGESTION IN THE HUMAN BODY 99 

4. Thoroughly chew a piece of dry bread or meat and observe and 
then describe in order the three movements of the lower jaw during the 
process of chewing food. 

5. In what part of each jaw are found the teeth that are used in 
grinding food? 

6. Examine one of the molars with the aid of a mirror and describe 
its grinding surface. 

7. How does the grinding surface of a bicuspid differ from that of 
a molar? 

The structure of a tooth. The three parts of a tooth (111. 
below) are the crown, or the portion that extends outside 






Crown* 



Neck 



^-Enamel 



^-—Dentine 



—-Pulp 



Root 




-Gum 



,-^ — Cement 



— Root canal 

Nerve and 
'i&^-f'ljii blood vessels 



Section of molar tooth 



Redrawn from Walter 



the gums, the neck, just at the edge of the gums, and the root 
or roots, which are imbedded in the upper or lower jawbone. 
The materials of which a tooth is composed are well shown 



100 PREPARATION OF FOODS FOR USE 



in a vertical section on page 99. The crown is covered with 
a layer of enamel, which is the hardest substance in the body 
and likewise very brittle. This enamel is thickest over the 
biting or grinding surface, gradually becoming thinner down 
the exposed sides, and disappearing altogether in the neck 
region of the tooth. In this region begins the bony cement, 
which completely incloses the roots. Within the enamel and 

the cement is the 
bony dentine, and 
this forms the 
greater part of the 
tooth. In the cen- 
tral part is the pulp. 
This region is sup- 
plied with nerves 
and blood vessels, 
which enter through 
small openings at 
the tip of each root. 
The blood furnishes 
the pulp of the teeth 
with nutrition. 

How the teeth are 
placed. Within the 
mouth cavity the 
solid food is cut into small pieces, mixed with the juices of 
the mouth, and then ground into a pulpy mass. A large 
part of this work is done by the teeth, which are set in two 
semicircular arches (111. above). In a normal set of teeth 
each grinding tooth in the lower jaw works against two cor- 
responding teeth in the upper jaw, and this is very necessary 
in order to chew the food properly and to keep the teeth and 
gums in a healthy condition. If, however, the teeth are not 




From Angle's •' Treatment of Malocclusion of the Teeth ' 

Proper arrangement of the teeth while chewing 
This is a remarkably good set of teeth. 






FOOD DIGESTION IN THE HUMAN BODY 101 

developing regularly as shown on page 100, a competent 
dentist should be consulted and his advice followed. 

The temporary and the permanent teeth. The first of 
the temporary teeth make their appearance at about six 
months of age, and at about the end of the second year the 
entire set of twenty temporary teeth is in place. Each one 
of these is later replaced by a permanent tooth, commencing 
at about six years of age. At this time the first of the 
permanent molars comes through the gums just back of the 
last temporary tooth on each side of the jaws, above and 
below. These teeth do not replace temporary teeth ; hence, 
they are the first teeth to appear in these locations. For this 
reason they are often mistaken for temporary teeth. 

These first permanent molars are the most important of all 
the teeth, and therefore they should be watched and guarded 
against decay with the utmost care. Just back of these 
first molars, at about twelve years of age, come the second 
molars. At the extreme rear the third molars, or wisdom 
teeth, erupt at about eighteen years of age. Often, how- 
ever, they appear at a later time, and somet mes not at all. 

In spite of the fact that the temporary teeth are shed, it 
is important that cavities appearing in any one of them 
should be filled in order to prevent their premature loss. 
If these teeth are lost at too early a time the space they 
formerly occupied is gradually closed, and the permanent 
teeth that are to replace them are forced into an irregular 
position. 

How the teeth should be cared for. Too much stress can- 
not be laid on the importance of proper daily care of the teeth 
as a means of avoiding decay. Neglect in this matter fre- 
quently results in pain, unsightliness of the mouth, and loss 
of the teeth. Certain disease conditions often result from 
unhealthy teeth. The teeth should be cleaned twice daily, 



102 PREPARATION OF FOODS FOR USE 

in the morning and before going to bed, in order to remove 
food particles that may be lodged in or between the teeth 
and also to remove films from the tooth surfaces. 

Cleaning the teeth may best be accomplished by a tooth- 
brush, small in size and with fairly stiff bristles, preferably 
using any reliable tooth powder or paste. Gritty powder 
or paste should be avoided. All surfaces of all the teeth 
should be carefully brushed by making as small a circular 
movement as possible with the ends of the bristles held 
firmly against the teeth. An excellent method is to begin 
with the teeth farthest back in the mouth and proceed 
from tooth to tooth on the outside surfaces around to the 
end tooth at the other side of the jaw, then returning to the 
starting point along the inner surfaces. Follow the same 
plan with the teeth of the other jaw. In this way no surface 
of any tooth will be missed and each surface will be thor- 
oughly brushed. The edge of the gum will also receive a 
gentle friction, which is an excellent way to keep its blood 
circulation active. The one thing to be avoided is a violent 
cross motion of the brush from one tooth to another, which 
in time causes damage to the delicate edge of the gum and 
makes it recede. 

There is no way in which decay can start except by the 
lodgment of bacteria on the tooth surfaces. The bacteria 
decompose any food present, producing acid that :;ray soften 
or dissolve the enamel unless protective substances are 
present in the saliva, otherwise, a cavity will be formed in the 
tooth. Brushing cannot clean the surfaces between the teeth. 
These can be reached, however, by drawing dental floss back 
and forth between the teeth. It is never wise to use the teeth 
to crack nuts or to bite similar hard substances. The enamel 
may in this way be easily broken or cracked, and if this 
happens, it is never replaced by the growth of new enamel. 



FOOD DIGESTION IN THE HUMAN BODY 103 

It is an error to believe that false teeth are as effective as 
the natural teeth. The crushing power of such teeth is 
vastly less than that of the normal teeth, which reduces their 
efficiency in chewing food. A very wise precaution is to 
have the teeth examined twice yearly by a dentist, who can 
detect the beginning of cavities and remove any accumula- 
tion of tartar. Tartar is an accumulation of lime material, 
derived from the saliva, that lodges on those portions of the 
teeth just at the margin of the gums. This irritates the 
delicate gum margin and is the most frequent cause of bleed- 
ing of the gums. Its continued accumulation in time brings 
about a detachment of the gum at the neck of the tooth with 
subsequent infection, and finally results in the loosening of 
the teeth. 

Importance of the vigorous use of the teeth. We are all 
more or less familiar with the fact that all the tissues of the 
body require exercise to keep them in a healthy condition. 
The vigorous use of the teeth in chewing our food brings 
about an improved blood circulation of the bone and the 
gums that support the teeth. Too much of our food is so 
soft that no such chewing is required to prepare it for 
swallowing. In addition this food readily lodges in the 
spaces between the teeth, and remains in the depressions. 
It is this tendency to lodge, and stick, and undergo decom- 
position in inaccessible places that chiefly brings about tooth 
decay. We should, therefore, instead of these soft food 
materials take a liberal supply of coarser foods that require 
more chewing. This would not only bring about a better 
circulation of the blood in the bone of the jaw, but would 
also help to keep the surfaces of the teeth in a clean, polished 
condition through the scouring action of the coarser foods. 

How the alimentary canal is fitted to carry on its functions. 
The general structure of any part of the food tube will be 



104 PREPARATION OF FOODS FOR USE 



made clear if we study a diagram of a section of the stomach 
(111. below), which with modifications will apply to the walls 
of the throat, gullet, and intestine. In the first place, the 
whole tube is lined with a thin covering of cells known as the 

mucous membrane. 




— Inner surface 

of the stomach, 

showing the 

openings of 

the gastric 

glands 

Gastric glands 

-Layer beneath 
the mucous 
membrane, 
containing 

many 
blood vessels 

y* Layers of 
muscle 



s Outer coat of the stomach (peritoneum) 
Section of stomach wall 
Which layer causes the food to mix with gastric juice ? 



This is kept moist 
by a slimy liquid 
known as mucus, 
secreted by the mu- 
cous cells. The mu- 
cous layer and the 
digestive juices that 
are poured into the 
alimentary canal 
provide a slippery 
surface over which 
the food can readily 
be moved. In the 
mucous layer of the stomach and small intestine there are 
numerous digestive glands the ducts of which open on the 
inner surface of these organs. 

In the second place, outside this mucous membrane is a rich 
supply of thin-walled tubes, mainly blood vessels known as 
capillaries (kap'i-la-riz, from the Latin, meaning hair, since 
they are so tiny) , which are well fitted to take up, or absorb, 
the liquefied food as soon as it is ready for diffusion through 
the tissues of the body. 

In the third place, layers of muscle constitute a consid- 
erable portion of the walls of the tube. By their con- 
traction these muscles mix the food with the digestive 
juices and gradually force the food onward in its course. 
Let us now get a general picture of the whole process of 
digestion. 



FOOD DIGESTION IN THE HUMAN BODY 105 

Digestion in the mouth. In the mouth food is cut up 
and ground into very small pieces and at the same time mixed 
with saliva. Thorough chewing (mastication) of food is 
very important since in this way the saliva is brought into 
intimate contact with the food particles. In this process 
the soluble sugars and minerals are dissolved and we thus 
get the taste of the food, which not only adds to one's enjoy- 
ment but also stimulates the flow of saliva. Meanwhile 
the ptyalin in the saliva changes a little of the cooked starch 
to malt sugar (maltose), thus giving additional flavor to the 
food. The food is now easily swallowed, and the muscular 
contractions of the gullet quickly force this soft, moist mass 
of food down to the stomach. 

Digestion in the stomach. Meanwhile, the good taste 
and odors of the food and the chewing movements of the 
jaw have caused the gastric glands in the walls of the stom- 
ach to pour out the gastric juice through the thousands of 
tiny openings of the ducts in the stomach. If the gastric 
juice were to come into contact with all the starch particles, 
the salivary enzyme (ptyalin) would have no further diges- 
tive action. But this does not seem to be the case. For a 
varying length of time, therefore, the ptyalin continues to 
act on some of the starch, thus changing it to malt sugar. 
The gastric juice, however, continues to pour out and the 
food is mixed with it by the muscular contractions of the 
walls of the stomach. Gastric juice is largely water, but it 
contains two ferments, pepsin and rennin, and enough hydro- 
chloric acid to make it quite sour, as you may have noticed 
when food has been forced into your mouth from the stom- 
ach some time after you have finished a meal. The rennin 
causes the protein in the milk to form soft curds. Rennin 
has no digestive action. However, by this change in milk, 
protein is retained in the stomach longer, since liquids are 



106 PREPARATION OF FOODS FOR USE 



very quickly forced into the small intestine. The pepsin 
now begins the digestion of casein and any other protein that 
may be present in the food, provided the food has been acidi- 
fied by the hydrochloric acid. Now when starch becomes 
acidified, saliva has no further action on it. 

You may wonder why all food does not flow at once from 
the stomach into the small intestine. If the part of the 

stomach next to the 
small intestine were an 
open tube, the food 
could not be kept in 
the stomach any more 
than it can be kept in 
the gullet when one 
swallows. This part of 
the stomach is kept 
closed by circular mus- 
cles, except at intervals 
when the muscles relax, 
the tube opens, and 
food is forced out by 
the contractions of the 
stomach. This end of 
the stomach is called 
the pylorus (pi-lo'r^s), 
which is the Greek word for gatekeeper. At intervals some 
of the acid mixture of food containing undigested starch, 
malt sugar, partly digested proteins, and undigested fats is 
forced into the small intestine, until finally the stomach is 
emptied of its contents. 

Digestion in the small intestine. As soon as the partly 
digested food from the stomach enters the small intestine, 
the bile from the liver and the pancreatic juice from the 




2)uodenum 



A section to show the interior of part of the 
alimentary canal 

Notice the circular ridges in the small intestine 
that delay the onward movement of the food. 
How do they help in absorption ? 



FOOD DIGESTION IN THE HUMAN BODY 107 

pancreas are poured over it ; the intestinal glands in this 
part of the intestine also give out their secretions, and the 
three secretions are mixed with the food by the muscular 
contractions of the walls of the small intestine. Now these 
three digestive juices act continuously and together, but 
digestion in the intestine will be easier to understand if we 
take up the action of each juice separately. 

Let us begin with the action of the pancreatic fluid. This 
extremely important secretion contains three digestive 
enzymes. One of these is a fat-digesting ferment. But 
strange to say, this ferment needs the help of the bile to do 
the work of changing fats so that they can be absorbed and 
later used. A second ferment is a protein-digesting enzyme 
which continues the action of pepsin on proteins ; and a 
third ferment is a pancreatic diastase, much more active 
than the ptyalin of the saliva, which changes both raw and 
cooked starch to malt sugar. Bile contains no digestive 
ferment, but, as we have already said, it aids one of the 
enzymes of the pancreatic juice in digesting fat. 

Now while the pancreatic juice and bile are digesting fats 
and the pancreatic juice is partly digesting proteins and 
changing starch to malt sugar, the intestinal juice is also in 
action. This digestive fluid has to finish the work of diges- 
tion begun by the saliva, gastric juice, and pancreatic juice. 

So you see complete digestion requires much cooperation on 
the part of these several digestive agencies. Thus intestinal 
juice completes the work of saliva and pancreatic juice in pre- 
paring starch for absorption and use, it completes the diges- 
tion of protein begun by gastric juice and pancreatic juice, 
and alone digests cane and milk sugars ; while pancreatic 
juice and bile acting together digest fat. And so the greater 
part of each food substance is finally changed to a form that 
can be absorbed by the blood and utilized by the body. 






108 



PREPARATION OF FOODS FOR USE 



Vein 



Lacfeal 



Absorption of foods from the alimentary canal. All the 

changes that have been described thus far are necessary 
before the food can really enter the body ; that is, pass 
through the various membranes into the capillaries that 

carry the blood. While it is 
possible that a certain amount 
of absorption may take place 
before the food reaches the in- 
testine, this amount is probably 
small. In the small intestine, 
however, all conditions are 
favorable for absorption : 
(1) the digestion of the avail- 
able food materials is here al- 
most wholly completed ; (2) the 
food lies for a considerable time 
in contact with a thin, moist 
membrane, beneath which are 
the thin- walled tubes (capilla- 
ries and lymph tubes) that are 
to absorb it ; and (3) the small 
intestine of an adult is about 
twenty feet long, and its inner 
surface is still further consider- 
ably increased by a succession 
of circular ridges and depres- 
sions (111. p. 106) and by mil- 
lions of microscopic projections known as villi (vil'i, singular, 
villus) (111. above). 

The digested fats are quite largely absorbed by the villi. 
In each villus there is a special tube known as a lacteal 
(lak'te-al), into which the digested fats pass. Lacteal is 
derived from a Latin word meaning milk. These tubes are 




Vein 



Lac tea/ 

"Artery 

Section of a villus 

Four million of these villi project 
from the inside wall of the small in- 
testine. What two kinds of tubes in 
the villi absorb digested food ? 



FOOD DIGESTION IN THE HUMAN BODY 109 

so called on account of the milky appearance of their con- 
tents when a meal containing much fat has been eaten. The 
digested starches (grape sugar) and the digested proteins are 
absorbed very largely by the capillaries not only in the villi, 
but also throughout the mucous membrane of the small 
intestine. The lacteals are a part of a system of tubes 
known as the lymphatic system. The substances taken in 
by them, including digested fats, are carried by the tubes 
of the lymphatic system and poured into the blood system 
near the heart (111. p. 126). 

As the food proceeds through the small intestine, portions 
are absorbed when they are completely digested. Hence, 
the bulk of a given meal of food tends to become less and 
less, and by the time it enters the large intestine practically 
all of the available carbohydrates, proteins, and fats have 
been absorbed from the alimentary canal. The rather solid, 
indigestible substances that remain consist largely of the 
cell walls of plants, the tough fibrous parts of animal foods, 
and any undigested food substances. This residue should 
be regularly expelled from the body each day, for, if this 
waste material is allowed to accumulate, it decays, and, as a 
result of this decay, poisonous substances are almost sure to 
be formed and absorbed into the blood with serious results. 
The following are among the best ways of preventing this 
condition, which is known as constipation: (1) the drinking 
of liberal quantities of water (as much as half a dozen glasses 
each day), which tends to keep the intestinal contents from 
becoming too solid ; (2) the eating of an abundance of vege- 
tables, especially salads, fresh fruits, and breads made of 
whole wheat or Graham flour. 

The foods mentioned above furnish bulk because they 
contain indigestible material like the cellulose of plants. 
This indigestible material is often called roughage, not be- 



110 PREPARATION OF FOODS FOR USE 

cause it is rough, but because it is not digested and absorbed 
as starches, fats, and proteins largely are, and so remains 
until expelled. Starches, fats, and proteins might still be 
undigested, that is, not digested, but they would not be 
indigestible, because they can be digested. (" Indigestible " 
means incapable of digestion.) 

Why hygienic habits of eating are necessary. One 
should form the habit of eating slowly and of thoroughly 
masticating each mouthful of food, for in this way the food 
is thoroughly broken up and thus is prepared for rapid 
digestion not only in the stomach but in the intestines as 
well. One also gets greater enjoyment from the good flavors 
released by longer chewing of the foods. This good flavor 
may be inherent in the food or it may be developed by partial 
digestion as when starch is changed to malt sugar by saliva. 
The process of chewing likewise stimulates the flow of saliva. 
Saliva not only helps to digest food, but also, when swallowed 
with the food, continues for a time the digestion of starch in 
the stomach and likewise stimulates to greater activity the 
glands in the walls of the stomach. 

The proper digestion of food depends in a large degree 
upon one's mental state. Experiments with animals and 
man have shown clearly that feelings of anger or worry stop 
the flow of digestive juices and the contraction of the mus- 
cular walls of the alimentary canal. Disagreeable topics 
should, therefore, be forgotten as far as possible while one 
is eating, and the mealtime should be made a season of enjoy- 
ment. " Laugh and grow fat " and " A merry heart doeth 
good like a medicine " are proverbs based upon sound prin- 
ciples of hygiene. 

It has likewise been proved experimentally that digestive 
juices tend to be given off more freely at regular and stated 
intervals. Regular hours of eating, therefore, are of great 



FOOD DIGESTION IN THE HUMAN BODY 111 

importance, for nothing more commonly deranges the diges- 
tive system than the continual nibbling of foods or sweets 
between meals. One should refrain from vigorous exercise 
or study for a time at least after eating ; walking, on the 
other hand, and other forms of mild exercise seem to 
promote digestion. 

QUESTIONS AND APPLICATIONS 

1. State two reasons why starches, fats, and proteins in the foods 
eaten are of no use to the body until they have been digested. 

2. What are two principal functions of the alimentary canal? 

3. Name the longest part and the widest part of the alimentary canal. 

k4. What is the function of the digestive glands ? 
5. What do digestive juices contain that make them so important in 
the digestive process? By what organs are the digestive juices made? 

6. Describe the parts by which the digestive juices reach the alimen- 
tary canal. 

7. (a) Name and locate three kinds of digestive glands found in the 
walls of the alimentary canal, (b) What is the name of the juice secreted 
by each? (c) State where each is poured out upon the foods. 

8. (a) Name, locate, and describe two digestive glands outside the 
walls of the alimentary canal, (b) What is the name of the digestive juice 
secreted by each of these glands? (c) Where do these two mingled juices 
first come in contact with the foods? 

9. Name the food substances that the combined action of all the 
digestive juices helps to prepare for distribution and use. 

10. State your observations and conclusions after testing saliva and 
then cooked starch for a reducing sugar. What was your final conclu- 
sion? 

11. What substance in saliva acts upon cooked starch and what sub- 
stance in plants has a similar action ? 

12. How do the cheeks and tongue act to keep the food between the 
teeth? 

13. Describe the three movements of the lower jaw while grinding food . 

14. Describe the grinding surface of a molar tooth. 

15. Why should the temporary teeth be cared for just as well as the 
permanent teeth ? 



112 PREPARATION OF FOODS FOR USE 

16. What part of the tooth is wholly covered by enamel and what part 
is only partly covered ? 

17. In what part of a tooth is blood present? Why is blood necessary 
in a tooth ? 

18. Give directions for removing with dental floss food particles from 
between the teeth. 

19. Give specific directions for brushing the teeth, with reasons for 
each. 

20. In what ways can your dentist help you to preserve an efficient set 
of teeth ? 

21. Why is it important that one should eat some foods that require 
thorough chewing? 

22. How is diet important in the development of the teeth? 

23. How are each of the following parts of the alimentary canal useful : 
(a) mucous membrane ; (6) digestive glands in the walls ; (c) muscles ; 
(d) capillaries? 

24. What food substances are partly or wholly digested in each of the 
following cavities, and by what digestive juices : (a) mouth ; (b) stomach ; 
(c) small intestine? 

25. Why cannot saliva continue to act as long as it is in the stomach ? 

26. How does each of the following adapt the small intestine for ab- 
sorption of digested foods: (a) length; (b) circular ridges; (c) villi? 

27. (a) How and where do digested fats get into the blood stream? 
(6) Through what layers must digested proteins and carbohydrates pass 
to get into the blood ? 

28. What is roughage, and why is it important in our foods? 

29. State and explain five good results that may come from thorough 
chewing of food. 

30. What has one's mental state to do with proper digestion of food? 
How do you know? 

31. Why is it better for one to eat at stated times? 

32. If you were to follow merely your tastes in choosing your diet, what 
mistakes would you be likely to make ? 

33. Find the reason for the name Graham flour. 



UNIT IV. HOW THE NEEDS OF THE CELLS 
ARE SUPPLIED 

PROBLEM 1. HOW IS CIRCULATION CARRIED ON IN 
THE HUMAN BODY? 

The Composition and Uses of Blood 

How we know that food substances are circulated in the 
human body. We have traced the course taken by the 
various food substances from the time they enter the mouth 
until they have been digested and absorbed through the thin 
walls of the tiny capillary blood vessels in the walls of the 
intestines. Microscopic capillaries are found not only in the 
lining of the alimentary canal but also in practically every 
other part of the body. We know this to be true because 
even a slight cut or pin prick results in a flow of blood, except 
in the outer layers of the skin and the nails. 

We can prove that food materials are distributed by this 
means, for if blood taken from any part of the body is tested 
for the different food substances, all classes of them are 
found to be present, though in slightly different proportions. 
In general, we may say that the liquid portion of blood, 
known as blood plasma, contains the following : 

Water 90 + per cent 

Proteins 8 + per cent 

Fats, sugars, and mineral matter 2~ per cent 

Thus we see that the food materials that were absorbed from 
the alimentary canal are available for use in every tissue 
of the body. It is evident, then, that there must be some 

113 



114 HOW THE NEEDS OF CELLS ARE SUPPLIED 



White corpuscles 




Red corpusch 

seen on edge, 

are run together 

in rows 



Red 

seen from 
the side 



means of transporting throughout the body the food sub- 
stances that are absorbed from the alimentary canal. The 
system of organs that carries on this function of distribu- 
tion is known as the circulatory system. 

How oxygen is circulated in the human body. Not only 
must the cells of our bodies be supplied with food for growth 

and repair and for fuel, but also a 
•/•,-.. supply of oxygen must be made 

available in each cell in order to re- 
lease the needed energy. Now in 
what way is this oxygen carried? 
When we examine the blood with 
the compound microscope, we find 
floating in the liquid blood plasma 
countless numbers of tiny bodies 
known as red corpuscles and white 
corpuscles (111. at left). Each red 
corpuscle is disk-shaped and hol- 
lowed out on both surfaces ; that is, 
it is biconcave. 1 When they are spread out in a thin layer, 
each corpuscle has a faint yellow color. On a slide, how- 
ever, these corpuscles have a way of arranging themselves 
like a pile of coins ; and when the mass is sufficiently great, 
the red color becomes evident. 

Microscopic study fails to show the presence of a nucleus 
in any of these red corpuscles. Red corpuscles are being 
destroyed all the time and new corpuscles are being sent into 
the blood from the red marrow of bones where they are con- 
stantly being produced. In the red marrow these cells 
contain a nucleus, but by the time they enter the blood the 

1 A model of a red corpuscle can be easily made from a small ball of putty, 
dough, or modeling clay, by flattening it between two pieces of wood, and then 
pressing in the two surfaces between the thumb and forefinger. For a description 
of white corpuscles, see p. 355. 



Red and white blood cor- 
puscles 



CIRCULATION IN THE HUMAN BODY 115 

nuclei have disappeared. We may, then, regard each red 
corpuscle as a modified cell, specially adapted for distributing 
oxygen. These corpuscles are able to do this because they 
contain a protein compound known as hemoglobin (he'mo- 
glo'bin), in which iron is present. This compound has the re- 
markable power of uniting chemically with oxygen, wherever 
this element is plentiful, to form a bright red compound called 
oxyhemoglobin (ok'si-he^mo-glo'-bm) . When oxygen is lacking 
in any part of the body, the oxygen needed is given off by 
this oxyhemoglobin. Thus it comes about that when the red 
corpuscles pass through the working tissues that lack oxy- 
gen, the oxygen is given up, the oxyhemoglobin is thereby 
reduced to hemoglobin, and the blood becomes a dark red or 
maroon in color. When the hemoglobin again comes in 
contact with an abundant supply of oxygen in the lungs, it 
changes to oxyhemoglobin, and the blood once more becomes 
bright red in color. 

It is scarcely possible to picture to ourselves the enormous 
number of red corpuscles in human blood. It may help 
somewhat to state, as Dr. Percy Stiles suggests, that about 
5,000,000 corpuscles would fill a space the size of a coarse 
grain of granulated sugar ; yet, if it were possible to repre- 
sent the total surface of corpuscles in our own blood that 
is exposed to oxygen, it would equal the total area of four 
baseball diamonds. What a wonderful provision for ab- 
sorbing and distributing oxygen ! 

The Organs of Circulation 

How the blood is kept in circulation. Since blood is 
continually flowing through the capillaries in all parts of the 
body, there must be a system of supply pipes bringing the 
blood to the capillaries. These are known as arteries 
(111. p. 128) . Then, in order to carry away the blood from the 



116 HOW THE NEEDS OF CELLS ARE SUPPLIED 



capillaries of any part of the body, there must be another set 
of blood vessels. These are known as veins. Finally, in 
order to keep the blood in constant motion through the 
arteries, capillaries, and veins, considerable pressure is re- 
quired. This pressure is exerted by a hollow muscular 
organ, the heart, which acts as a force pump, and by the 
contraction of the elastic material in the walls of the arteries. 
While some of the facts relative to the movement of the 
blood in the body had been known for many centuries, it re- 
mained for William Harvey, 
an English physician (111. 
at left), who lived about 
three hundred years ago, to 
demonstrate that there is a 
complete circulation of the 
blood . By this we now mean 
that blood which is forced 
from the heart through the 
arteries, thence into the cap- 
illaries, is then brought back 
to the heart through the 
veins. Harvey's work has 
proved to be one of the most 
far-reaching discoveries that 
has ever been made in biol- 
ogy. We are now to study somewhat in detail the various 
organs of circulation. 

The size, shape, and position of the heart. The heart is 
an organ about the size of one's fist and is shaped somewhat 
like an inverted cone with a blunt apex (111. p. 117). It lies 
behind the breastbone, near the middle of the chest cavity, 
with its more pointed end, or apex, extending toward the left 
side opposite the interval between the cartilages of the fifth 




William Harvey (1578-1657) 
What did Harvey demonstrate ? 



CIRCULATION IN THE HUMAN BODY 117 



and sixth ribs. Since the beat of the heart is felt most 
plainly near the apex, it is commonly but wrongly believed 
that the heart lies entirely on the left side of the body. Let 
us imagine the front wall of the chest cavity to be removed ; 



Main veins ^ 



Aorta 



Bronchial 
tubes -„ 

Right 
auricle 4 — 



Ribs- 




Gall- 
bladder 



Liver'' 



Large * 
intestine 



Large 

intestine 



Small " 
intestine 

Bladder 

Organs of chest and abdomen 

we should then see the soft pink lungs on either side and, 
between them, the heart (111. above). 

The structure and the action of the heart. If we should 
examine the upper part of the heart, we should note on either 
side a rather thin-walled sac (111. p. 118). These two cham- 



118 HOW THE NEEDS OF CELLS ARE SUPPLIED 

bers of the heart are known as auricles. Now what is the 
use of the auricles, and why are there two of them? We 
have already learned that blood is returned to the heart from 
all parts of the body by means of veins. These veins empty 
into the auricles. To the left auricle is brought by four 



Aorta—^^^^ 



Pulmonary 
/ artery 



Superior 
vena cava 

Pulmonary < 
veins 



Right — 
auricle 

Semilunar ~- 
valves 

Inferior — 
vena cava 



Right ventricle 




^Pulmonary 
' veins 

Left 

auricle 

Valves between 

auricles and 

ventricles 

---Left 
-ventricle 



Aorta 



Structure of the heart 
The arrows indicate the course of the blood to, through, and from the heart. Note 
the complete separation of the " right heart " from the " left heart." Why should the 
wall of the left ventricle be thicker than the wall of the right ventricle ? 



-pulmonary veins all the blood that comes from the lungs, 
while to the right auricle by means of two large veins comes 
the blood from all other organs of the body. 

If we should squeeze the lower part of the heart, we should 
find it to be firmer and much more muscular than the thin- 
walled auricles. Likewise the walls of the left ventricle 
would be found to be much thicker than those of the right. 



CIRCULATION IN THE HUMAN BODY 119 



A cross section of the heart about midway shows the pres- 
ence of two chambers in this lower region, which are known 
respectively as the right ventricle and the left ventricle. Each 
ventricle lies immediately below and is connected with an 
auricle by means of an opening. 

The blood from the veins, after entering the right or left 
auricle, passes downward through the opening into the cor- 



Auricle^ 



Semilunar valves 
(closed) 



^Auricle 




■Semilunar 
valves 
(open) 



- Ventricle 



Valve from 

auricle to 

ventricle 

(open) 

Ventricle - 

Valve from auricle to 
ventricle (closed) 

Action of the valves of the heart 
At left, the position of the valves when the blood is flowing from auricle to ventricle ; 
at right, the position of the valves when the blood is forced out from the ventricle into 
the large artery. 

responding ventricle, until the two ventricles are nearly filled. 
Each auricle then contracts somewhat, thus distending the 
ventricles with the added blood. The walls of the more mus- 
cular ventricles now begin to close in upon the blood they have 
received, and we might naturally expect this blood to be 
forced back into the auricles. Such would be the case, were 
it not for the presence of flap-shaped membranes which form 
each of the valves between the auricles and the ventricles. 
These valves are now forced upward into a horizontal posi- 
tion, thus closing the opening into each auricle (111. above). 



120 HOW THE NEEDS OF CELLS ARE SUPPLIED 

Leading out from each ventricle is a large artery ; the 
artery from the right ventricle (pulmonary artery) carries 
blood to the lungs, and the artery from the left ventricle 
(aorta) divides into branches that send blood to all the other 
organs of the body. After the valves guarding the entrance 
from the auricles have been closed, the ventricles continue to 
contract and force out the blood which they contain into 
the aorta and pulmonary arteries. When the ventricles are 
emptied and begin to relax, the blood that has been driven 
into the distended arteries would naturally flow back into 
each ventricle, if it were not prevented from doing so by three 
pocket-shaped membranes at the entrance of each artery, 
which fill out and thus block the openings from the ventri- 
cles. On account of the shape of these pockets (like that of 
a half -moon), they are known as semilunar valves. 

Location of the arteries. Arteries may be defined as blood 
vessels that carry blood away from the heart toward the capil- 
laries. The smallest arteries connect with the capillaries. 
Every time the ventricles contract, the arteries leading 
from them are expanded, and this is true of every artery 
in the body. Most arteries lie beneath thick layers of 
muscle or beneath bones, which protect them from possible 
injury. In certain regions of the body, however, they lie 
close enough to the surface to be felt. Place the forefinger 
on the inner surface of the thumb side of your wrist. Do you 
feel a distinct throbbing called the pulse f This is caused by 
the enlargement of the artery at each heartbeat, followed 
by a similar decrease in size. Consequently, when an artery 
is cut, the blood is forced out in spurts at each contraction of 
the ventricle. 

The structure and the use of the arteries. When a piece 
of an artery of a higher animal or of man is examined, it is 
found that this blood vessel retains its tubular form, due to 







CIRCULATION IN THE HUMAN BODY 121 

the presence of thick layers of muscular and elastic tissue 
(111. below). In the large arteries the walls are composed 
almost wholly of elastic tissue. When the blood is forced 
into them by the contraction of the ventricles, these arteries 
are expanded. The 
elastic walls then 
squeeze the blood 
forward toward the 
capillaries. 

In the smaller ar- 
teries, in addition tO Cross section of an artery Cross section of a vein 
the elastic tissue, Comparison of structure of an artery and a vein 
the Walls Contain Which of the three layers of an artery differs most 
i , • i • i from the corresponding layer of a vein ? 

muscle tissue, which y 

can relax or contract. This muscular tissue in the walls of 
these smaller arteries regulates the diameter of these blood 
vessels and so determines the relative amount of blood sup- 
plied to any particular organ. For example, when the face is 
flushed, the muscles in the tiny facial arteries have relaxed 
more than is usual and so have permitted an additional 
amount of blood to be forced into the arteries in this region of 
the body. Pallor is caused by contraction of the muscular 
walls in the small arteries of the skin, which is not followed 
by the usual amount of relaxation ; hence the normal amount 
of blood cannot be forced through these arteries. Under 
ordinary conditions the muscles in the walls of the arteries 
are neither contracted nor relaxed to their fullest extent. 
Rather their usual condition is midway between, in each pulse 
beat. The action of these arterial muscles, as well as that of 
all muscles, is regulated by the nervous system, but this action 
is in no direct way under the control of the will. 

One of the mistakes in regard to the circulation made by 
those who studied it before Harvey's time is evident from 



122 HOW THE NEEDS OF CELLS ARE SUPPLIED 

the name " artery." The earlier workers found these large 
blood vessels empty after death, and so they supposed they 
were air tubes; hence the name " artery " was given (from 
the Greek, meaning windpipe) . The arteries contract after 
the heart has ceased to beat, and so the blood is forced out 
into capillaries and veins. This explains why arteries are 
found empty when life has become extinct. 

EXERCISE 33 

How is the pulse rate affected by increasing the degree of muscular 
activity? Home experiment. 

Place the forefinger of the right hand on the inner surface of the 
wrist of the left hand, as directed above. While sitting quietly, count 
the pulse for a minute, being careful not to miss any of the beats. Re- 
peat the count several times, until you get an approximate agreement 
in the number of beats a minute. (Do not use this count in 2 below.) 

1. When you are -sure you can count your pulse beats accurately, 
lie down for a few moments and completely relax your muscles. Now 
count the pulse rate for a minute, repeating the count as before. Tell 
what you have done and record your result. 

2. In a similar way make a record of your pulse while you are sitting 
still. 

3. Determine likewise the pulse rate when you are standing. 

4. Take some vigorous exercise for several minutes (e.g. setting-up 
exercises, running up stairs, or riding a bicycle). Now determine and 
record your pulse rate. 

5. What do you conclude, therefore, as to the effect on your pulse 
rate of increasing degrees of muscular activity? 

Position, number, and structure of the capillaries. As we 
trace the arteries farther and farther from the heart, we see 
that they divide and subdivide until very small branches are 
formed. That these fine branches are still arteries is proved 
by the fact that muscular and elastic tissue are present in 
their walls. Finally, however, these tiny blood vessels 



CIRCULATION IN THE HUMAN BODY 123 




Capillaries 



Network of capillaries 

These small blood vessels are shown connecting a 

small artery with a small vein. 



become continuous with still smaller tubes, the capillaries. 
So numerous are the capillaries that one cannot push the 
point of a needle for 
any considerable dis- 
tance into any organ 
of the body without 
piercing a number of 
them (111. at right). 
These smallest of 
blood vessels commu- 
nicate freely with one 
another and form a 
complicated network 
of tubes that bring 
blood close to all the 
cells of the body. 

In structure the capillaries are extremely simple. At the 
points in the blood system where arteries end and capillaries 
begin, muscular and elastic tissues disappear. Indeed the 
walls of capillaries are formed only of a single layer of very 

thin-walled cells (111. at left). 
We have in this arrangement 
one of the best possible condi- 
tions for the process of osmosis, 
as we shall now see. 

Why the capillaries are so 
important in the circulatory 
system. If the blood were kept 
constantly within a system of 
thick-walled tubes like the ar- 
teries, even though continu- 
ally in circulation, it would be unable to help in the nutrition 
of the cells, since osmosis through such thick walls would be 





Surface view Section 

Structure of capillaries 

Note that the walls have the thickness 

of only one cell. 



124 HOW THE NEEDS OF CELLS ARE SUPPLIED 



Lymph tube 



impossible. Not only must each cell somehow get from the 
blood the food materials and oxygen it needs for its special 
work, but the blood must also secure the food and oxygen 
and give off the wastes in the organs of excretion. Ex- 
changes like these are possible only through the thin walls 
of tubes like capillaries. 

What lymph is. From our discussion of the structure and 
use of the capillaries, one might infer that the liquid food 

substances of the blood 
Capiiiancs pass directly from the 
thin-walled capillaries 
into the tissue cells and 
that waste substances 
are given off from the 
cells directly to the 
blood. Though in gen- 
eral terms this is what 
happens in the capillary 
regions, still in our dis- 
cussion of this process 
we must take into ac- 



Tissue cells 




Capillaries ' 
Lymph tube 



Lymph tube 



Lymph spaces and tubes 
Note the intimate relation of the lymph to the 
cells and to the capillaries and lymph tubes. The 
arrows indicate the direction of flow of blood and 
of lymph. 



count the presence of a watery, colorless liquid known as 
lymph, which surrounds practically every cell of the body 
(111. above) . As the blood passes through the capillaries, part 
of the plasma diffuses out and thus forms the liquid to which 
we have just referred. One may say, therefore, that lymph 
is blood minus the red corpuscles. The " water " that is 
squeezed out of a blister is practically like lymph in its 
composition. 

Changes that take place in the lymph. Lymph, then, is 
always found between the walls of the capillaries and the 
tissue cells. In other words, the cells of the muscles, glands, 
and other organs live surrounded by lymph. It is obvious, 






CIRCULATION IN THE HUMAN BODY 125 

therefore, that lymph acts as a medium of exchange — 
a middleman, so to speak — between the blood in the capil- 
laries and the liquid in the cells. The food and oxygen by 
osmosis get out of the blood into the lymph and thence into 
the cells. In a similar way, but in a reverse direction, the 
waste products which every cell must get rid of pass from 
the cell through the lymph into the blood. Hence, while it 
is true that the blood gives up its supplies of food and oxygen 
to the cells and takes in at the same time the waste ma- 
terials, all these changes take place through the lymph, 
which, on one side, is in direct contact with the capillary 
walls and, on the other, bathes the cells in its fluids. 

How a surplus of lymph is returned to the blood circula- 
tion. Lymph is derived both from the blood and from the 
cells. Hence there is a constant tendency for it to increase 
in quantity. The question may now be asked — What be- 
comes of this excess of lymph? If there were no provision 
for draining it off, the tissues would become unduly dis- 
tended. Such is the case in the condition known as dropsy, 
in which the excess liquid has to be drawn off by " tapping " 
the body where the excess accumulates. 

Let us now see how it is that this valuable liquid reenters 
the blood stream. The lymph spaces between the cells in the 
various tissues contain tiny thin-walled tubes known as 
lymphatics; these gradually unite, forming larger and larger 
tubes, and finally collect the lymph into two tubes which 
empty into veins in the neck region (111. p. 126). There are 
small valves along the course of the lymphatics that prevent 
the lymph from taking a backward course. 

Position and structure of the veins. The blood that 
comes from the capillaries returns to the heart through the 
veins. Veins may be seen on the back of the hand as a 
branching system of blood vessels. Many veins, like those 



126 HOW THE NEEDS OF CELLS ARE SUPPLIED 

on the hand, lie near the surface, while most of the arteries 
are deeply buried among the other tissues. Unlike the 
arteries, veins have no pulse. 

When the veins are emptied of blood, they immediately 
collapse. This is due to the fact that their walls have far 




Left vein from head 

Left vein from arm- 

Superior vena cava^ 
Heart 



-Thoracic duct • 



Liver 



„-- Inferior vena cava 



Vein from 

stomach 



> Lymph vessels in 
lumbar regions^. 



Intestine 



Paths of absorbed food from the 

human digestive tract. P^n of distribution of the 

Proteins and carbohydrates chief lymphatic vessels 

by Veins; fats by lymphatics From Walter's " Vertebrate Zoology ' 

Plan of blood vessels and lymph vessels that absorb the digested food 
Where does the main lymph duct pour the lymph into the blood system ? 




CIRCULATION IN THE HUMAN BODY 127 



Vein laid open 

to show the shape 

of the valves 



less muscular and elastic tissue than have the walls of the 
arteries (111. p. 121). Veins are provided with valves shaped 
much like the semilunar valves at the mouth of the large 
arteries leading from the heart ; consequently the blood can 
flow only toward the heart, for as soon as it begins to flow in 
the opposite direction, these 
valves are immediately filled, 
and the passage is closed (111. 
at right). 

Course taken by the blood 
through the body. Having 
now completed our survey of 
the structure and action of 
the heart and of the blood 
vessels, we are ready to study 
the blood system as a whole 
and to learn how the blood 
goes to, through, and from 
the various organs of the body, 
of a drop of blood from the time it leaves the left ventricle 
until it again returns to this chamber of the heart. 

When the left ventricle contracts, the blood is forced out 
into the aorta, which is the largest artery of the body. This 
blood vessel forms an arch (111. p. 118), from the upper por- 
tion of which branches extend to the head and the arms. The 
aorta then continues downward through the chest and ab- 
dominal cavities, supplying on its way the various organs 
of these regions (111. p. 128). It then divides into two arteries 
that continue down the legs. Each of these larger arteries 
that we have mentioned divides again and again, until 
finally the blood is forced through a network of very fine 
capillaries in the various organs to which the capillaries 
extend. 



Section of Section of vein 

vein showing valve 

showing closing to prevent 

the open backwa rd flow 

valve of blood 



Interior structure of a vein 
The arrows indicate the direction of 
blood pressure in the veins at various 
times. 

Let us now follow the course 



Diaphragm 



Aorta — 
intestine 



K/dney 



/ Vein from head 
yArtery to head 

Ve/n from arm 
'Artery to arm 




General course of the blood through the body 

Arteries are shown in white ; veins in black. Which part of the blood circulation is not 

shown in this diagram ? 



CIRCULATION IN THE HUMAN BODY 129 

From these capillaries blood passes into tiny veins, which 
carry all the blood into larger veins and finally empty it into 
two large veins, one from the upper part of the body, the 
other from the lower part of the body. These two veins 
empty into the right auricle of the heart. Thence the blood 
passes into the right ventricle. 

The right ventricle by its contraction drives the blood 
through the pulmonary artery to each of the lungs, where its 
many branches finally reach the countless capillaries in the 
interior of these organs. Many tiny veins now receive the 
blood from the capillaries and convey it to the left auricle, 
by the four pulmonary veins, whence it flows downward into 
the left ventricle. About one minute is usually required for 
blood to complete this circuit from the left ventricle back to 
this chamber of the heart. 

Circulation and Excretion 

Waste matters in man. When carbohydrates and fats 
are oxidized in the cells, carbon dioxid and water are finally 
formed. When proteins are oxidized, nitrogenous com- 
pounds such as urea are formed in addition to carbon dioxid 
and water. All these substances are known as waste mat- 
ters, or excretions. The process of getting rid of waste matters 
by living things is known as excretion (from a Latin word, 
meaning to sift out). 

The organs of excretion in man. The four principal 
organs in man that are concerned in the process of excretion 
are : the lungs, the kidneys, the skin, and the intestines. 
The principal work of the lungs in excretion is to rid 
the blood of excess of carbon dioxid, although considerable 
water is also excreted. The kidneys are especially con- 
cerned in the elimination of water and urea contained in 
the plasma. 



130 HOW THE NEEDS OF CELLS ARE SUPPLIED 

The skin also eliminates some water, a slight amount of 
urea, a little carbon dioxid, and some minerals, principally 
salt. However, as we shall see, the skin is not primarily 
an organ of excretion. The intestines excrete a small amount 
of nitrogenous matter from the blood through the mucous 
membrane. Also a certain amount of waste matter is given 
off into the intestine from the liver in the bile. The un- 
digested and indigestible substances expelled from the large 
intestine are merely the refuse from the food, and therefore 
are not, strictly speaking, excretions. 

How the kidneys are adapted for excretion. The kidneys 
are two dark red bean-shaped organs located on either side 
of the spinal column, just below and behind the stomach 
(111. p. 128). The tissue of a kidney consists of a great 
number of very long, narrow, crooked tubes in coils known 
as tubules (tu'bulz) (111. p. 131, B). The wall of a tubule is 
formed of a single layer of cells and is in close contact with 
capillaries. As the blood passes through the capillaries of 
the kidneys the cells of the tubules remove from the blood, 
water, nitrogenous waste (mainly urea), and mineral salts 
(mainly common salt). All these wastes constitute a liquid 
known as urine. On the inner or concave side of each 
kidney there is a funnel-shaped cavity into which the liquid 
wastes flow from all the tubules (111. p. 131, A). From 
this funnel-shaped cavity in each kidney the urine enters a 
single duct called the ureter which conveys the excretion to 
a muscular bladder, which is an organ of temporary storage. 
At more or less regular intervals the urine is discharged 
from the bladder through a passage known as the urethra 
(u-re'thrd) (111. p. 94). 

The amount of urine excreted will depend largely upon 
the quantity of water contained in one's food and drink. 
The urea and mineral salts are more nearly constant in 



CIRCULATION IN THE HUMAN BODY 131 



amount, though this will vary somewhat with the amount 
of protein and salt eaten. It must be evident, then, how 
necessary it is to drink plenty of water each day in order 
that the excretion of urea and minerals may not be hindered. 
On the other hand, excessive drinking of liquids, such as 
beer, is very likely to harm the kidneys. There seems to be 
no danger of excessive drinking of clear water. Overeating 




Cortical 
region-. 

/ Pelvis 

{cavity of kidney) 

-Renal artery 

-.-Renal vein 



-^Ureter 



! Cortex 

Pyramid of medullary 
region 

A. Section of Kidney 



Medullary 
region 



Tip ofpyramid / 
B 




•From renal 
artery 

Capillaries 



x To renal vein 



'"Collecting 
tubules 



Course of Tubules 
of Kidney 



The internal structure of a kidney 

of protein foods throws extra work upon the kidneys, which 
may also do them harm. If the amount of urine excreted 
is scanty and highly colored, it is evident that more water 
is needed in the body. 

How the skin is adapted for excretion. The particular 
organs of excretion in the skin consist of innumerable tubes 
not unlike those found in the kidneys. They are quite 
generally distributed through the skin. The inner end of 
each of these tubes is much coiled and this constitutes the 



132 HOW THE NEEDS OF CELLS ARE SUPPLIED 



,' Surface por< 



Epidermis 



part known as the sweat gland. In close connection with 
the sweat glands are capillaries. The cells of the sweat 
glands secrete from the capillaries water, minerals (mainly 
salt), and a very little urea. These substances make up the 
excretion known as sweat, or perspira- 
tion. The perspiration is forced out 
through the tubes to the surface of the 
skin (See 111.). 

How other animals excrete liquid 
wastes. In all the vertebrates, that is, 
animals that have a spinal column 
(" backbone "), we find more or less 
definite bodies known as kidneys, con- 
taining small tubules supplied with 
capillaries as in man ; and in all the 
hairy animals, namely, the mammals, 
which are more closely related to man, 
we find very definite kidneys which in 
structure and function are much like 
those in man. 

Changes in the composition of the 
blood. The composition of the blood 
is continually changing while it is pass- 
ing through the capillaries of the vari- 
ous tissues and organs. In every tis- 
sue of every organ the blood in the 
capillaries gives up to the lymph oxy- 
gen and food materials and in turn 
receives from the lymph wastes (carbon dioxid, water, 
and urea) formed by the oxidation of food substances. In 
certain organs other changes in the composition of the blood 
occur which may be made clearer by presenting them in the 
tabular form which follows : 




Secreting 
cells 



^Capillaries 

A single sweat gland 
with duct 

What kind of blood ves- 
sel makes possible the 
elimination of perspiration 
by the gland cells ? 



CIRCULATION IN THE HUMAN BODY 133 



Specific Changes in the Composition of the Blood 



Organs Affected 


Blood Loses 


Blood Gains 


Digestive glands of mouth, 


Materials needed for 




stomach, intestine, and ab- 


the manufacture of 




domen 


digestive juices 




Lining of stomach and intestine 




Water and digested 
food substances 


Lungs 


Carbon dioxid and 
water 


Oxygen 


Kidneys and skin 


Water and urea 





Hygiene of the Blood and of the Circulatory 

Organs 

Conditions that affect the red corpuscles. Since supply- 
ing oxygen to the various tissues is the function of the red 
corpuscles, it is very important that their number be suffi- 
cient and that they be kept in a healthy condition. To this 
end an abundance of sleep, fresh air, exercise, and nutritious 
foods are the essential conditions. Every one knows that the 
face looks pale after loss of sleep or when food or fresh air is 
insufficient or during periods of physical inactivity, and this 
appearance indicates a lack of red corpuscles. Habitual 
paleness may indicate anemia, which is a disease requiring 
medical treatment. 

Conditions that affect the blood plasma. All the nutrition 
of the tissues is finally derived from the blood, and all the 
food substances of the blood come from the foods that we eat. 
If these foods are insufficient or of an improper kind, the 
plasma will of course be deprived of necessary ingredients, 
and the organs must inevitably suffer in consequence. 

Effect of exercise on the heart. The pulse rate is slowest 
when we are asleep. As the activities of the day begin, the 



134 HOW THE NEEDS OF CELLS ARE SUPPLIED 

heartbeat is quickened, and after violent exercise this organ 
may beat as rapidly as twice a second. Exercise, when 
properly regulated, is undoubtedly beneficial to every organ 
of the body. Hence the heart should be kept in such a 
vigorous condition that it is ready to meet not only the 
ordinary requirements of everyday life but also the strain 
that may come in such emergencies as escape from threaten- 
ing danger or recovery from disease. 

It is possible, however, to overstrain the heart muscle by 
exacting from this organ too violent or too prolonged activity. 
Such may be the case in sprinting or in long-distance runs or 
in certain strenuous games, e.g. football. These sometimes 
result in permanent harm to the walls or the valves of the 
heart. Before a youth takes part in violent athletic con- 
tests, he should be examined by a -competent physician. 

Effect of exercise on the blood vessels. When one is 
using the muscles actively, greater oxidation in the tissues 
goes on, and a larger amount of blood is needed to supply the 
oxygen and foods, and to remove the wastes formed by this 
increased oxidation. The muscular walls of the small ar- 
teries relax in the muscles or other organs that are especially 
active, thus supplying these organs with more blood. A 
greatly increased supply of blood cannot be secured in several 
organs at the same time. This is the reason why it is un- 
hygienic to carry on vigorous physical or mental activity 
immediately after a hearty meal. 

How bleeding from wounds may be stopped. If the 
blood flows in spurts, an artery has been cut. Send for 
a doctor and proceed at once to stop the flow of blood, 
otherwise it may be too late when he arrives. With the 
fingers or thumb press firmly upon the severed artery be- 
tween the wound and the heart until the flow of blood 
ceases. If the wound is in the upper part of the arm or leg, 



CIRCULATION IN THE HUMAN BODY 135 




a device known as a tourniquet (toor'ni-ket) may be used. 
An improvised tourniquet (111. below) may be made with 
a handkerchief or a neckerchief by tying it loosely around 
the limb, and placing a pad or a 
smooth stone wrapped in a cloth 
underneath the tourniquet and 
over the artery where pressure has 
been successfully applied. Then 
pass a pencil or stick through the 
loop in the knot and twist it until 
the pressure on the artery is suf- 
ficient to stop the flow of blood. 
If expert aid has not been secured 
within half an hour, it will be 
necessary to apply a bandage over 
the wound and gradually release 
the pressure on the artery, thus 
permitting the flow of blood to the 
tissues ; otherwise serious results to the tissues beyond the 
wound may ensue. After a few minutes if bleeding con- 
tinues, the pressure may be again applied on the artery. 

When blood flows evenly from a wound, it is an indication 
that a vein has been cut. In such cases a sterile pad should 
be placed over the wound and pressure applied by means of a 
bandage. 1 

Bleeding from the nose can usually be stopped by lying 
down and placing a wad of wet cotton or paper inside the up- 
per lip or applying ice or cold water to the bridge of the nose. 

Clotting of blood. When a blood vessel is injured and the 
blood escapes, it gradually thickens to form a dark red mass 



Improvised tourniquet applied 
to the upper arm 

a, b indicates the course of the 
inner artery of the left arm. 
What takes the place of a pad in 
this tourniquet ? 



1 For detailed directions for first aid in case of wounds see American Red Cross 
Abridged Textbook on First Aid, 3d rev. ed., 1925. For treatment of slight cuts 
see page 353. 



136 HOW THE NEEDS OF CELLS ARE SUPPLIED 

having the consistency of jelly. This jellylike mass is called 
a blood clot, and the process by which the clot is formed is 
known as clotting. The immediate cause of clotting is due 
to the formation of microscopic threads composed of fibrin. 

There are four factors in the plasma that are concerned 
in the formation of fibrin. The first is the protein fibrinogen 
(fl-brin'6-jen), the fibrin maker. The second is a fibrin 
ferment which under certain circumstances changes the 
fibrinogen to fibrin. The third is a compound of calcium 
without which the ferment cannot act on the fibrinogen, 
and the fourth consists of cells smaller than red blood cells 
known as platelets (plat 'lets). Under normal conditions no 
coagulation occurs, but if a blood vessel is injured and 
blood escapes, the platelets are decomposed and a substance 
is formed which makes it possible for the fibrin ferment in 
the presence of a calcium compound to change the fibrinogen 
to fibrin. The threads of fibrin form a mesh of fibers which 
entangle the red and white corpuscles and thus form the clot, 
which in turn stops the flow of blood if the pressure of the 
blood stream is not too great. Clotting is of great physio- 
logical importance, since it provides a natural means of closing 
injured blood vessels, thus preventing undue loss of blood. 

The rapidity with which fibrin is formed varies with dif- 
ferent people. Anyone whose blood clots very slowly or 
not at all is in constant danger of bleeding to death from 
any slight injury. Persons so afflicted are called " bleeders," 
and this tendency is known as hemophilia (he'mo-fil'i-d, from 
the Greek, meaning blood-loving). No permanent remedy 
for hemophilia has yet been found since the cause is unknown. 

A COMPLETION TEST 

In your notebook, write the numbers given below, and after each number 
write the word or words necessary to complete each of the statements. 






TRANSFER OF MATERIALS IN PLANTS 137 

Plasma is found in (1). The substance most abundant in plasma is 
(2). The food substance second in abundance in plasma is (3). A func- 
tion of the red corpuscles while in the capillaries of the lungs is to (4). 
In the capillaries of the tissues, the red corpuscles give off (5) and absorb 
some (6). Hemoglobin is found in the (7). Hemoglobin absorbs oxygen 
wherever it is (8) and gives it up wherever it is (9). The name of the 
man who first demonstrated a complete circulation of the blood is (10). 
The principle function of the auricles is to (11). The principal function 
of the ventricles is to (12). The color of the blood in the right auricle is 
(13), because it lacks (14). Blood in the heart flows from (15) to (16). 
The blood vessels that help force the blood toward the capillaries are 
called (17). The blood vessels that carry the blood to the heart are called 
(18). The blood is pumped toward the lungs from the chamber of the 
heart called the (19) through branches of a blood vessel called the (20). 
The part of the heart that receives blood from the lungs is called the (21). 
The blood is pumped toward all parts of the body except the lungs from 
the part of the heart called the (22). Blood in the heart is prevented 
from flowing backward from (23) into (24) by means of the (25) that open 
toward the (26). Valves at the beginning of the pulmonary artery and 
aorta prevent blood from flowing back into the (27). Valves in veins 
allow blood to flow only toward the (28). The blood vessels in which 
changes in composition of blood occur are called (29). To stop the flow 
of blood from a bleeding artery, the pressure should be applied on the side 
of the wound (30) . In the capillaries of the mucous membrane of the small 
intestine, the blood receives water and (31). In the tissues the blood 
loses (32), water, and (33) and gains (34) and (35). 

PROBLEM 2. HOW ARE PLANTS ADAPTED FOR THE 
TRANSFER OF MATERIALS? 

Why further study of the structure of plants is necessary. 
On pages 73-74 we learned that water and soluble min- 
eral matter must move from the soil into the roots and 
upward through the stems to the leaves, while the man- 
ufactured food must move from the leaves to the roots. 
We have also perceived that carbon dioxid must either en- 
ter the leaves directly or be absorbed, as are mineral matter 
and water, by the roots and then carried upward with the 



138 HOW THE NEEDS OF CELLS ARE SUPPLIED 

water to the leaves. We have, however, had no visible 
proof that any of the movements of these materials actually 
occurs, nor have we learned anything as to how the various 
parts of a plant are adapted by structure to carry on the 
work of absorption and distribution. In order, therefore, 
to get a better understanding of these matters, we shall now 
try to get some first-hand knowledge of the structure of 
roots, stems, and leaves, and follow each study with a 
demonstration of the parts of the plant through which 
materials pass upward. We should then be better able to 
understand the adaptations of roots, stems, and leaves for 
the functions of absorbing and distributing the necessary 
materials from the soil and air. 

EXERCISE 34 

What is the general structure of roots ? Laboratory study. 

Select the largest roots of a well-developed bean seedling (Windsor 
bean, if possible) or the roots of corn or of common weeds. With the 
thumb and finger nail gently scrape off the outer layers from part of a 
piece of one of these roots. When no more of this material can be 
removed easily by this method, pick with a pin the central part of 
the root, which is left, so as to separate the fibers. The outer layer 
you have removed is composed largely of the cells of the cortex, and the 
central part that has been exposed is called the central cylinder (111. 
pp. 139, 146). 

1. Describe what you have found. 

2. Which is composed of the tougher and harder material, the cortex 
or the central cylinder? 

3. Of what do you find the central cylinder to be composed? 

4. Make an enlarged diagram of a lengthwise section of a piece of 
root to show the cortex and the central cylinder. Label : Cortex, 
Central cylinder, Fibers of central cylinder. 

EXERCISE 35 

Through what parts of roots do liquids pass upward ? Laboratory 
experiment. 



TRANSFER OF MATERIALS IN PLANTS 139 



Place some corn or Windsor bean seedlings or weeds in water that 
has been colored with red ink or eosin powder so that only the lower 
ends of the roots are in the liquid. After several hours or on the next 
day cut some cross sections of these roots above the point where they 
were in contact with the ink. Examine the cross section of the root 
prepared in this way. 

1. Describe the experiment 
as it was performed. 

2. Through what part of 
the root (cortex or central cyl- 
inder) has most of the liquid 
passed? How do you know? 

3. Make a sketch about an 
inch in diameter of the cross 
section of the root, to show the 
colored and colorless portions. 
Label : Part of the root through 
which liquid traveled, Unstained 
portion of root, Cortex, Central 
cylinder. 




Epidermis 

1— Cortex 

—Food - con- 
ducting 
tissue 

-Water - con- 
ducting 
vessel 



What the absorbing 
organs of roots are. You 
have doubtless taken it 
for granted that roots 
must somehow take up 
the water from the soil, 
but have you any idea 
how they are able to do 
it? You will remember 
that when you scraped 
off the outer layer of a young root, you found it was composed 
of a very soft material which, for that reason, was easily re- 
moved. Is it not clear, therefore, that these cells must have 
very thin walls? The outer layer of these cells would, of 
course, be in close contact with the moist earth. What proc- 



-- Growing 
point 



-Root cap 



From Transeau's " General Botany" 

Structure of a root tip 
The various parts are greatly magnified. 



140 HOW THE NEEDS OF CELLS ARE SUPPLIED 

ess, therefore, could quite easily be carried on by means of 
these cells ? But this is not all. The very outermost layer 
of cells which you removed with the cortex are not only like 
the cortex in having thin walls, but they also produce slender 
outgrowths which are especially well fitted for absorbing soil 
water. The outermost layer of cells of a root is called the 
epidermis or skin of the root, and the outgrowths from the 
epidermal cells are the root hairs. 

EXERCISE 36 

What are root hairs like and where on the roots do they form? 

Laboratory study. 

To the teacher: Root hairs may be grown for study as follows: 
Cover the bottom of as many Petri dishes as are needed with a layer 
of blue blotting paper. Soak the paper with water and lay several 
grains of soaked barley, oats, or corn upon the bottom of each dish. 
Put the covered dishes in a warm place for several days. When 
the root hairs have developed, wipe the moisture from the inside 
of the covers, quickly replacing the latter. If Petri dishes are not 
available, two clean pieces of window glass of any convenient size 
may be used instead. Cover one of the glasses with layers of wet 
blotting paper, put the soaked grains in position, and cover with the 
second glass, fastening the two together with threads or strings. 
Stand one end of the preparation thus made in a jar with enough water 
to reach the lower edge of the blotting paper. 

Examine first with the naked eye and then with a hand magnifier 
the roots of sprouted grains, developed as described above. Notice 
tiny outgrowths from the sides of the roots ; these outgrowths are 
the root hairs. 

1. Look at the very tip of the root and state whether root hairs 
are there present or absent. 

2. State whether the root hairs are longest near the tip or in the 
direction of the grain. 

3. Make a drawing much enlarged to show the shape of one of the 
roots including the root tip and the various lengths of root hairs. 
Label : Root tip, Root hairs. 



TRANSFER OF MATERIALS IN PLANTS 141 



Cell sap 



Layer of 
protoplasm 



How roots are fitted to absorb soil water. You will 
remember that the outside layer of the root consists of soft 
material that is readily scraped off. It is evident that soil 
water must pass through this layer in order to enter the 
central cylinder. One may readily surmise that the soil 
water enters the thin-walled cells on the outside of the 
root, and this surmise is correct. But since some of these 
cells are specially fitted for this 
process of absorption, we need to 
study this root structure somewhat 
more in detail. 

When we examined the roots of 
young seedlings that were germi- 
nated on moist blotting paper in a 
Petri dish (111. p. 70), we found that 
the roots were covered with thou- 
sands of tiny outgrowths which we 
have called root hairs (111. p. 70). 
When a thin, lengthwise section of 
such a root is looked at with a com- 
pound microscope, each root hair is 
found to be an outgrowth of certain 
cells found in a single layer of thin-walled cells covering the 
cortex (111. p. 146). This single layer is the epidermis of the 
root. Most of the soil water enters through these root hairs, 
and we are now to see how they are adapted for this purpose. 

Inside the thin cell wall of each root hair (111. above) is a 
lining of protoplasm, and the rest of the root hair is filled 
with cell sap, which contains minerals and perhaps sugar 
and protein in solution. Root hairs especially lend them- 
selves to the process of osmosis, since we have here two 
liquids, namely, soil water and cell sap, separated by two 
membranes, the permeable cell wall and the lining of proto- 




Nucleus 



Two root hairs 
This illustration represents 
highly magnified sections. 
Which part has a selective action 
during osmosis ? 



142 HOW THE NEEDS OF CELLS ARE SUPPLIED 

plasm which has a selective action. Now the soil water 
consists of a high percentage of water and a low percentage 
of a number of soluble minerals. The cell sap will have a 
lower percentage of water than the soil water since it con- 
tains soluble food substances, such as sugar and protein, 
which are not in the soil water at all. Cell sap will also 
contain soluble minerals but usually in a lower percentage 
than in the soil water. 

Now it must be evident that since the water in the soil 
has a greater concentration than the water inside the cell, it 
will move or pass through the membranes into the root hair 
where the percentage of water is less. Each soluble mineral 
in the soil water will tend to pass through the membranes into 
the root hair as long as the percentage of that particular 
mineral is greater outside. The soluble sugar and any other 
soluble food substance in the cell sap will tend to pass through 
membranes into the soil water since there is no sugar or pro- 
tein in the soil water. Botanists have shown, however, that 
practically only the inward movement of soil water occurs. 
The outward flow of the dissolved substances is prevented 
by the layer of protoplasm. Thus we see that protoplasm 
forms a membrane that has a selective function. 

By a similar osmotic action water and soluble minerals 
pass from the cells of the epidermis to the cells of the cor- 
tex, and from these cells to others, until these substances 
reach the central cylinder. The compounds then move 
upward through the central cylinder, as we proved by plac- 
ing the tips of roots of seedlings in colored water (Exercise 35). 

EXERCISE 37 

What is the general structure of herbaceous ) stems ? Laboratory 
study. 

1 Herbaceous plants are those that develop little wood as do the plants known 
as herbs, such as spinach or ragweed. 



TRANSFER OF MATERIALS IN PLANTS 143 

To the teacher: Cut off a sufficient number of pieces from the stems 
of weeds {e.g. pigweed or ragweed) or of a well-developed bean seedling 
or of a geranium so that each member of the class may be supplied with 
material. 

Study an herbaceous (weed, bean, or geranium) stem as follows: 
With the tip of the knife blade peel off the thin layer known as the 
epidermis. Beneath this layer scrape off with the knife edge a green, 
pulpy layer, the cortex, until you come to a fibrous layer. With a pin 
strip the fibrous layer into threads. In the center of the stem pick out 
with a pin the soft material, the pith. 

1. Describe what you have done and state the kind of material you 
find in each region of an herbaceous stem. 

2. Make an enlarged drawing of a lengthwise section through the 
middle of the herbaceous stem. Label the drawing as a whole and 
each of the four regions. 

3. If time permits, make an enlarged drawing of a cross section of 
the annual stem and label as directed in 2 above. 

EXERCISE 38 
What is the general structure of a woody stem ? Laboratory study. 

To the teacher: Secure pieces of a young stem of a maple, lilac, or 
other woody stem that shows the three layers of bark. Split some 
pieces lengthwise in halves. 

1. Peel off the outer covering, the bark, from a piece of the stem 
till the wood is exposed. The bark of a young stem usually consists 
of three more or less distinct layers. 

a. With a knife gently scrape off an outer or brown bark, and expose 

a dark green layer known as the green bark. Scrape this until 
you come to a more or less tough layer known as the fibrous 
bark or bast (which may be slightly green). Describe each of 
these barks as to position and color. 

b. Pick into threads the fibrous bark. In what direction of the stem 

do the fibers run ? By breaking strips of each layer determine 
which of the three barks is toughest. 

2. Feel of the wood from which the bark has just been removed. 
Describe the substance which covers the wood, after scraping off a 
little with your thumb nail. This is the cambium or growing layer, 



144 HOW THE NEEDS OF CELLS ARE SUPPLIED 

which produces the new wood on its inside surface and bark on its 
outside surface. When the bark is torn off, the cells of this layer are 
broken and the slimy protoplasm oozes out. 

3. By means of a penknife or pin dig into the wood and also into 
the pith at the center of the stem. State the relative position and 
hardness of the wood and the pith. 

4. With the aid of compasses make a diagram, at least three inches 
in diameter, of the cross section of a woody stem to show the relative 
thickness of the various layers. (These layers might well be repre- 
sented by different colors.) Label : Brown bark, Green bark, Fibrous 
bark or Bast, Cambium layer, Wood, Pith. 

EXERCISE 39 
What is the general structure of the corn stem ? Laboratory study. 

To the teacher: Cut pieces about two inches in length from full- 
grown cornstalks, and split each piece in halves. (If necessary, these 
pieces may be preserved from year to year in 4 per cent formalin or in 
70 per cent alcohol.) 

Examine the cross and longitudinal sections of corn stem. Find 
the rind (the outer layer), the woody bundles or fibers (threadlike 
structures), and the pith (material between the bundles). 

1. Thrust your pencil point into the pith. Is this material hard or 
soft? 

2. Pull out one of the woody fibers. Is it tough or tender? 

3. Push your pencil point into the rind. Is it hard or soft? 

4. Make a drawing (X 2) showing both cross and longitudinal 
surfaces. Label : Rind, Woody bundles, Pith. 

EXERCISE 40 

Through what parts of stems do liquids pass upward ? Laboratory 
experiment. 

To the teacher: Place the lower ends of some herbaceous leafy stems, 
some woody stems, and some corn stems in a strong solution of eosin 
in water or in red ink. Allow these stems to stand in the colored liquid 
overnight or until the color appears in the leaves. (When the leaves 
are on the stems, the liquid will move through the stems more rapidly.) 
Cut off above the level of the ink or eosin solution enough pieces of 



TRANSFER OF MATERIALS IN PLANTS 145 



each kind of stem to supply the members of the class, and split each 
piece lengthwise halfway. 

1. Describe the preparation of the experiment. 

2. Through what part of each kind of stem did the ink or the eosin 
rise ? How can you tell ? 

3. What do you conclude, therefore, as to the part of the herbaceous 
stem, the woody stem, and the corn stem through which soil water rises ? 

4. In your drawings of sec- 
tions of each of these stems made 
in Exercises 37, 38, 39, label : 
Part of stem through which red ink 
rose. 

EXERCISE 41 

What is the general structure 
of a simple leaf? Laboratory 
study. 

Examine a simple leaf, e.g. 
maple, geranium, or lilac, and 
note that it is made up of the fol- 
lowing parts : a leafstalk, which 
attaches the main part of the leaf 
to the stem of the plant, and the 
blade, the flat, expanded portion. 

1. How does the blade differ 
in form from the leafstalk ? 

2. Hold the leaf to the light. 
How many main veins do you 
find ? Where are they smallest ? 
By what are the main veins con- 
nected? 

3. Make a drawing, natural size, by tracing the outline of the 
leafstalk and blade. Draw carefully the principal veins and a few 
of their branches, being careful to show their relative size and 
their connections. Label : Leafstalk, Blade, Main veins, Branching 
veins. 

4. Pick to pieces one of the larger veins. Tell what you have done. 
Of what is this vein principally composed ? 




Horse chestnut Wild strawberry 

Various types of leaves 
Which are simple leaves, and which are 
compound ? 



146 HOW THE NEEDS OF CELLS ARE SUPPLIED 



,Baseof 

root hairs 



EXERCISE 42 

Through what part of leaves do liquids pass upward? Laboratory 
experiment. 

To the teacher: Place in red ink the lower end of a leafy branch of 
any vigorous plant, e.g. geranium or bean seedling, and allow it to 
stand in sunlight or a warm place until the red color appears in the 
leaves. 

1. Give an account of the experiment, stating your observations. 

2. What do you conclude as to the part of the leaf through which 
soil water is distributed to different parts of the blade ? 

3. In your drawing of a simple leaf (Exercise 41) label : Part through 
which colored water passed upward. 

How roots, stems, and leaves are fitted for carrying soil 
water upward. In all three of these organs of plants we have 

demonstrated the presence 
of fibrous material, which 
we have torn apart into 
threads. In the roots these 
fibers are found in the cen- 
tral cylinder (111. at left). 
In young herbaceous stems 
of many kinds of plants, the 
fibrous material is arranged 
in the form of a sheath of 
woody bundles that sur- 
round the pith (111. p. 152). 
In older stems of annuals 
and in woody stems these 
bundles increase in number 
and in size until they come so close to one another that they 
form an apparently continuous sheath, which in woody stems 
constitutes a large part of the stem. Finally, in leaves this 
fibrous material is limited to the leafstalk and veins. Our 




-> Epidermi 



Root hair 



Cross section of a root 
Through which part does soil water pass 
upward, and through which part does sugar 
pass downward? 



TRANSFER OF MATERIALS IN PLANTS 147 



dissections have shown that the woody bundles are continu- 
ous from the roots, through the stem, out into the veins of 
the leaves (Ex. 41), and our experiment with the red ink 
proves that this same material contains the passageways 
through which liquids readily 
pass upward. 

A different arrangement of 
woody bundles is shown in an 
herbaceous stem like the corn- 
stalk (See 111.). Such a stem 
is covered on the outside with a 
hardened rind, within which is 
the pith. The woody bundles 
in this kind of stem are scattered 
through the pith instead of being 
arranged in a sheath of bundles 
outside the pith as in the young 
woody stem. 

Let us now see why sap trav- 
els upward through the fibrous 
regions and not through other 
parts of the plant. In order to 
understand this, we need to 
know something of its micro- 
scopic structure. On examin- 
ing a thin lengthwise section 
of these woody bundles in root, stem, or leaf, we find scat- 
tered among other cells tiny tubes, or ducts, which are 
empty except when they are carrying sap (111. p. 148). It is 
easier to distinguish these ducts when they are separated 
from each other, as shown on page 148. Then we see that 
the walls of the ducts are frequently thickened and therefore 
strengthened by spiral threads or by rings. 




Courtesy of Brooklyn Botanic Garden 

Cornstalk 
The cut-away portion shows the 
threads, which are woody bundles. 
Irregular masses of pith can be seen 
between the woody bundles. 



148 HOW THE NEEDS OF CELLS ARE SUPPLIED 

Running parallel to and between these ducts are elon- 
gated, more or less sliver-shaped, wood cells, which have 
thick walls. These overlap each other at the ends and 
give toughness to the woody bundles wherever these are 
found. Since the ducts are seen only in fibrous material, 




Sieve 




Bast | / 

cells ! / \ !■"■«** wlls 

I / v 

[' Cambium cells 



Lengthwise section 
of sieve tube, 
showing edge 
view of sieve 



Wood 

cells Pith 



Duct 



Surf act view of v 
sieve plate «8&P* 
Note the perforations >M§ 



Lengthwise section of a sunflower stem 

it is evident that they furnish a ready means by which the 
soil water with its mineral matter passes upward through 
the plant. 

To determine whether a plant takes in more water than 
it can use. In preceding sections we have learned that water 
has many uses in plants. It contributes the greater bulk of 
material for the making of carbohydrates and protoplasm, 
and it serves as a medium by which mineral matter, oxy- 
gen, carbon dioxid, and sugar are distributed through the 
plant. 

Nor is this all. The growth of the plant and the upright 
condition of the leaves and young stems are also dependent 
on water. Does a plant take in more of this material than 
it needs for all these purposes? The following experiment 
will make plain the answer to this question. 



TRANSFER OF MATERIALS IN PLANTS 149 

EXERCISE 43 

Is water vapor given off by the leaves of a green plant ? Laboratory 
study. 

Wrap sheet rubber or thin oilcloth about a pot containing a vigorous 
plant after it has been thoroughly watered. Tie the rubber or oilcloth 




Couriesy of Brooklyn Botanic Garden 

Experiment to illustrate transpiration 

Flower pot at left placed near a window and beneath a bell jar ; picture at right, same 

plant after twenty-four hours. 

about the stem to prevent the escape of water from the soil (111. above). 
If rubber cannot be obtained, melted paraffin may be poured over the 
soil after the pot has been painted inside and out with hot paraffin. 
Cover the plant thus prepared with a large bell jar with the inner sur- 
face dry and stand it in the sun for a few hours. 

1. Describe the preparation of the experiment, stating the reason 
for the use of the rubber or paraffin. 

2. State your observations and conclusion. 



150 HOW THE NEEDS OF CELLS ARE SUPPLIED 

3. Why is the bell jar necessary? 

4. What becomes of the water vapor given off by the leaves of trees 
and of other plants ? 

What transpiration is and how it can be measured. In 

the preceding experiment we saw that even a small plant 
gives off, or excretes, sl considerable quantity of water. If we 
were to weigh the plant at the beginning and then at inter- 
vals, we might determine the exact amount of water given off 
each day. It has been estimated that large trees give off as 
much as 180 gallons daily. Multiply this by the thousands 
of large trees in a forest, and you will get some conception of 
the enormous amount of invisible water that is given off by 
plants. 

When water is given off as an invisible gas, the process 
is called transpiration. Not all the water, however, that is 
given off by plants is transpired. Under special conditions 
it may actually ooze out of the ends of the veins in tiny drops 
of water, as in the leaves of grape and young nasturtium 
plants or of lawn grass forming " dew." 

How leaves are fitted to allow the escape of water vapor. 
To understand how leaves are adapted for transpiration, we 
need to review the microscopic structure of leaves (p. 68). 
It will then be possible to understand how the transpiration 
of water from the leaf occurs. As we have shown, water 
from the soil is continually moving up through the ducts in 
the roots, stems, and leaves. Finally it comes into the cells 
surrounding the air spaces. The water must then pass 
through the thin walls of these cells into the air spaces. 
From the air spaces it may diffuse through the stomata into 
the outer air. 

One of the principal uses of the stomata is to afford a con- 
stant supply of carbon dioxid to the cells that contain chloro- 
phyll. Since carbon dioxid will be needed for starch manu- 



TRANSFER OF MATERIALS IN PLANTS 151 



facture in the daytime, the stomata must be open at a time 
when there would naturally be the greatest amount of 
evaporation or transpiration due to the heat of the sun. If 
this is true, it would seem that there should be developed 
some means for checking transpiration, provided photosyn- 







Chlorophyll 
bodies 



Guard cells'- 
Upper epidermis Lower epidermis 

Courtesy of Brooklyn Botanic Garden 

Epidermis of leaf of lizard' s-tail 
Compare this figure with the illustration on page 68. What differences do you find 
in the covering of the upper and lower surfaces of these leaves ? Why cannot carbon 
dioxid enter the leaf through the upper epidermis ? 



thesis is not interfered with. Such means are present, as 
we shall now see. 

How guard cells help to check transpiration. When the 
cells of the plant are fully distended (turgid) with water, the 
guard cells are likely to be in the same condition. This 
results in so changing the shape of the guard cells that the 
passageway, or stoma, between them is open wide. There- 
fore transpiration can go on readily if the conditions are 
favorable for evaporation ; that is, if the air is warm and dry. 

If, however, the air has nearly all the moisture it can hold, 
little transpiration can occur, no matter how widely open the 
stomata may be. Therefore plants will not wilt on very 



152 HOW THE NEEDS OF CELLS ARE SUPPLIED 

muggy days, even if the temperature is high. If, on the 
other hand, the plant cells, including the guard cells, are not 
well filled, the walls of the guard cells tend to come together, 
thus more or less closing the stomata and, to a certain extent, 
preventing the escape of moisture. However, this will not 
always stop transpiration sufficiently to prevent wilting. In 
fact, transpiration may go on until the plant droops. This, 
as we have stated, is very likely to occur in bright sunlight, 



Cortex 




J?pfderm/& 



-J>h/osm (bast) *\Fibro- 

\ vascu/ar 



Cambium (growing /ay ety ( (wooc/yj 
Xy/em (wood) J bund/e 



Structure of part of a cross section of stem of castor-oil plant 
In which part is soil water carried upward ? In which part is sugar carried downward ? 

for then the guard cells cannot close, even though other cells 
may have lost enough water to cause wilting. Hence we see 
that the guard cells are not altogether adapted to control 
transpiration. 

Structure of a woody bundle. In very young stems the 
fibrous matter is arranged as we have seen in detached 
bundles (111. above). These are known as fibrovascular 
(fl'bro-vas'ku-ldr) bundles, since each bundle always con- 
sists of at least two kinds of structures, namely, fibers for 
strength and tubes or vessels which are concerned with the 
distribution of soluble materials. The word vascular signi- 
fies a vessel for the conveying of fluids. Thus, the vascular 



TRANSFER OF MATERIALS IN PLANTS 153 

system in man consists of blood vessels. Now, in the 
bundle, the fibers are of two kinds, woody fibers and the 
fibers of the bast (111. p. 148). Likewise, the vascular part 
or the tubes are of two sorts : ducts, which are mingled 
with the woody fibers, and sieve tubes, which are distributed 
through the bast or phloem (flo'em) (111. p. 152). 

In all woody stems and in the greater number of herba- 
ceous stems there is a third layer of great importance between 
the other two. This layer consists of thin-walled cells called 
the cambium. It is the cambium that produces all the wood 
and all the bast and thus makes possible the growth of the 
stem in diameter. Stems like the cornstalk and lily stems 
have no cambium or growing layer in the bundles, and so are 
unable to grow to any considerable diameter. 

Early in the development of woody stems the bundles in- 
crease in number and finally practically join one another so 
that we find almost continuous rings of the three kinds of ma- 
terial, namely, wood on the inside next to the pith, bast on the 
outside, and between these two a very thin layer of cambium. 

In a woody stem the wood of the bundles is very evident 
and usually forms the greater part of the stem. The 
cambium consists of a very thin slimy layer that can easily 
be rubbed off the wood and bark when the bark is stripped 
from the stem. The bast forms the fibrous inner bark of 
such stems. The green soft layer of the bark, sometimes 
called the green bark, is the cortex which we find in all very 
young stems under the epidermis. 

Some of the changes that occur in the growth of a woody 
stem. In our discussion thus far, we have considered the 
adaptations of stems for exposing leaves to the light and for 
transmitting food materials to and from the leaves. But 
the stem has other important functions which we are now to 
consider. In a young twig, before the brown bark thickens 



154 HOW THE NEEDS OF CELLS ARE SUPPLIED 




and shuts out the light, the green bark, on account of the 
presence of chlorophyll, is enabled like the leaves to carry 
on the manufacture of carbohydrates. In a very young 

stem the surface is covered by 
thin epidermis which helps to 
prevent the undue escape of 
moisture. In this layer are 
stomata that allow the passage 
of gases that occur in the proc- 
ess of breathing or are needed 
in food manufacture. Later 
this epidermis is replaced by 
the outer or brown bark, which 
serves as a means of protection 
against unfavorable weather 
conditions and insects. In this 
brown bark the stomata re- 
ferred to above are developed 
into openings known as lenticels 
(len'tl-selz), which carry on the same functions. In an old 
tree the outer bark becomes very thick and corky and the 
green layer disappears entirely. 

The growth of the tree in thickness, as already stated, is 
due to the activity of a layer of cambium cells between the 
wood and the fibrous bark. In early spring the cambium 
cells, by rapid growth and division, form on their innermost 
surface a new layer of wood (which appears as a ring in cross 
section) and on their outer surface more fibrous bark. As 
the season advances, the activity of these cells becomes less 
and less, and finally growth ceases during the winter. 1 

Stems of plants like the corn, bamboo, and palm have no 
true cambium layer, and therefore even in the case of plants 

1 Sometimes trees form more than one layer during a season. 



Cross section of oak wood (magni- 
fied) 
Note the pith rays (vertical lines) 
and the varying thickness of the annual 
rings (horizontal lines). How do you 
explain this difference in thickness ? 



TRANSFER OF MATERIALS IN PLANTS 155 

of this type that live on from year to year no annual rings are 
formed. In the growth of these stems, new bundles develop 
in the pith between those already formed. 

In the preceding paragraph we have stated that the woody 
bundles in woody stems increase in number so that they 
practically meet. However, there are always a few cells of 
the pith that lie between the bundles. These thin layers of 
cells between the wood of the bundles extend out from the 
pith to the cambium in rays resembling somewhat the spokes 
of a wheel. These rays are known as medullary (med'^-la-rf) 
rays, or pith rays. Medullary rays are supposed to act as 
channels for the passage of soluble food across the stem and 
also for the storage of food (111. p. 154). 

How leaves, stems, and roots are adapted for carrying 
manufactured foods downward. Carbohydrate manufac- 
ture is carried on wholly in the green parts of leaves and stems 
and these materials must find their way to other parts of the 
plant (e.g. places of storage in fruits, seeds, stems, or roots). 
Through what channels, then, does this movement of food 
materials take place ? When we examine still further one of 
the fibrous bundles described on page 152, we find its outer 
region contains tubular cells somewhat different in appear- 
ance from the ducts already described. These tubes are 
called sieve tubes because perforated cross partitions, which 
remind one of a sieve or a strainer (111. p. 148) , appear at inter- 
vals along their course. Like ducts, these sieve tubes form a 
continuous system, beginning in the tiny veins of the leaves 
and extending downward through stem and root. It is 
through these tubes that food materials travel from their 
place of manufacture to regions of food storage. Sieve 
tubes, unlike ducts, contain a thin layer of protoplasm. 
When one strips off the bark of a woody stem, one finds its 
inner layer consists of white fibers, and it is in this layer of 



156 HOW THE NEEDS OF CELLS ARE SUPPLIED 

bark, the bast of the woody bundle, that sieve tubes are 
found. It is relatively easy to show that this region of bark 
is concerned with the downward movement of sap, for, when 
a wire is tightly bound around a twig or a tree trunk, a swell- 
ing, which is found to contain supplies of manufactured food, 
appears in the bark above the wire. If a ring of this fibrous 
bark is cut from around a tree trunk, the whole tree dies dur- 
ing the second year as a result of this girdling process, since the 
lower parts of the tree are cut off from their food supply. 

Summary of absorption and circulation in plants. The 
soil water which is first absorbed by the root hairs and other 
epidermal cells of the roots passes into the cells of the cortex, 
and thence into the ducts of the central cylinders of the 
various roots. It then moves upward through the ducts 
of the roots, through the ducts of the vascular bundles of the 
stems and the vascular bundles in the veins of the leaves. 
From the ducts of the leaves this soil water now diffuses 
through the walls of cells to supply all the cells of the leaves. 
In the green cells of the leaves the soil water and the carbon 
dioxid obtained from the air are used in the manufacture of 
sugar. This, in turn, is employed in making other foods. 

These foods then pass out of the cells where they are manu- 
factured into the sieve tubes in the bast of the vascular bundles 
of the leaf veins and so move on downward into the sieve tubes 
of the vascular bundles of the stems and roots, and thence into 
the living parts of these organs. Here the food materials may 
be used at once, or they may be stored away. It seems prob- 
able that the cells of the medullary rays may serve as a means 
by which the sap containing the foods may pass across the 
stem to reach the growing cells of the cambium layer. 

While it is evident that there is no complete circulation of 
the essential materials, such as occurs in the circulatory 
system of man, yet the ducts and the sieve tubes do act more 



TRANSFER OF MATERIALS IN PLANTS 157 

or less like definite channels as do our blood vessels, and thus 
expedite the passage of the nutrients and manufactured food 
materials from one part of the plant to another. 

QUESTIONS AND APPLICATIONS 

1. Tell what you found out by experiment regarding the structure of 
the cortex and the central cylinder of a root. 

2. Through which part of the root did the colored liquid pass upward ? 

3. Why were the roots sectioned above the point where they were in 
contact with the colored fluid ? 

4. From what layer of the root do the root hairs develop? 

5. In what ways are root hairs especially adapted for absorbing soil water ? 

6. Why will the flow of water and soluble minerals tend to move into 
the root hairs and other parts of the epidermis ? 

7. Why will soluble food substances ordinarily be unable to pass into 
the soil? 

8. Through what cells must the soil water pass in order to reach the 
central cylinder? 

9. Describe and name each of the four layers present in the herbaceous 
stem studied. 

10. Through what parts of the herbaceous stem used did the colored 
water rise ? 

11. How does the structure of the corn stem differ from the structure 
of the other herbaceous stem used ? What parts are similar in structure ? 

12. Name and describe the shape and structure of each of three parts 
of a simple leaf. 

13. Through what parts of the leaves did the colored water pass upward ? 

14. How are roots, stems, and leaves adapted to carry soil water upward ? 

15. How are wood cells adapted for the service they perform ? 

16. How are leaves, stems, and roots adapted to carry sugar downward ? 

17. What part of the fibrovascular bundles contains the tubes that 
carry the soil water upward and which part contains the tubes that carry 
sugar downward? Give the name of the two kinds of tubes. 

18. Where in the fibrovascular bundles of an herbaceous stem is the 
cambium found and what is its function? 

19. Describe the cambium in a woody stem and give its location. 

20. State the location and appearance in a woody stem of the medullary 
or pith rays. What is the probable function of these rays? 



UNIT V. RELEASE OF ENERGY IN LIVING 

THINGS 

PROBLEM 1. HOW ARE LIVING THINGS ABLE TO DO 

WORK? 

Some examples and a definition of work. If you were 
asked to give some examples of work, you might mention 
activities like the following : shoveling coal or snow, pushing 
a lawn mower or a carpet sweeper, or rid- 
ing a bicycle uphill. In each of these ac- 
tivities a body of matter is set in motion. 
It must be evident too that muscular effort 
is necessary to set the lawn mower in mo- 
tion and to keep it in motion. These life- 
less objects seemingly resist our efforts to 
move them. Whenever resistance is over- 
come, work is being done. Hence in all the 
activities named above work will be done 
since resistance is being overcome. 

Likewise, if we attempt to stop or re- 
duce the speed of a body that is in motion, 
it resists our efforts. Thus, if an auto- 
mobile is started, we find that, if we 
attempt to stop it, or cut down its speed, 
we must make an effort, since the car 
seemingly resists being stopped or slowed 
up. So work may be done by retarding or 
stopping the motion of a body. 

We may now ask whether work is carried 

158 




A radiometer 

What form of en- 
ergy made the blades 
revolve ? 



HOW LIVING THINGS WORK 



159 



&~Brain 



-'Nerves 



^^m-Electric 
,#f cells 



-*ji'iy 



■Spinal 
cord 



on by any agency other than man. If trains, trolley cars, 
tractors or elevators are to be set in motion and kept in 
motion, resistance on the part of these bodies of matter must 
be overcome, and therefore work must be done. Now let us 
see what it is that does 
the work in these cases. 

What energy is. The 
ability to do work or to 
overcome the resistance 
of a body so as either to 
cause motion or to re- 
tard or stop motion is 
known as energy. In 
briefer form, energy is 
the ability to do work. 
We may say, therefore, 
that it must be some 
form of energy that does 
the work or that over- 
comes the resistance in 
all the cases mentioned 
above. 

Some of the forms of 
energy in our environ- 
ment, and how they may be recognized. The movements of 
bodies of matter, either large or small, as in the examples 
named on page 158 furnish the clearest evidence that energy 
has been or is being expended. An electric current causes a 
fan to revolve or an elevator to rise or a trolley car to go. 
Therefore the electric current is a form of energy, since in 
overcoming resistance it is causing motion and so is doing 
work. Heat is a form of energy, for it enables a locomotive 
to pull a train. Heat from the burning fuel in the furnace of 




Torpedo fish 

Notice the hexagonal bodies (electric cells) that 

discharge electricity that causes shocks. 



160 RELEASE OF ENERGY IN LIVING THINGS 




Courtesy of Brooklyn Botanic Garden 

Exhibition of energy in plants 



the engine changes 
water in the boiler 
to steam. The ex- 
pansive energy of 
the steam imparted 
by the heat drives 
the engine. 

The radiometer 
(111. p. 158) is an in- 
strument which 
shows that light also 
is a kind of energy. 
This instrument con- 
sists of a small glass 
bulb within which 
are four thin metal 
blades mounted on 
a needle point so as 
to revolve like a 
windmill. One side 
of each metal plate 
is blackened. When 
this instrument is 
exposed to direct 
sunlight or electric 
light, the blades re 
volve rapidly. As 
the radiometer is 

The nasturtium seedlings 
are shown after three expo- 
sures to light for forty-eight 
hours : at the top, light from 
all sides ; in the center, light 
from right only ; at the bot- 
tom, light from left only. 






HOW LIVING THINGS WORK 161 

withdrawn from the source of light, the speed of the revolu- 
tion decreases, and in the dark motion ceases altogether. 
Since light causes motion or does work, it is a form of energy. 
Kinds of energy developed in living things. All the 
activities of our own bodies in which we use muscles (e.g. 
walking, running, lifting objects, playing the piano) are 
examples of muscular, or mechanical, energy. Our bodies 
and those of most living things also develop a certain amount 




After Stone 



Exhibition of energy in plants 
These fern plants in growing have broken their way through concrete. 

of heat energy. Fireflies and some marine animals give off 
light energy. Certain fishes (e.g. the electric eel and the 
torpedo fish [111. p. 159]) develop enough electrical energy to 
give a distinct shock to an animal as large as a horse. 

In plants, too, there are evidences of mechanical energy. 
Examples that may be cited are the opening and closing of 
leaf buds and flower buds, the movement of leaves toward 
the light (111. p. 160), the pushing of roots through the soil. 
Indeed we may have noticed that heavy flagstones of a 
sidewalk have been lifted by growing plants (111. above), or 
that rocks have been split apart by the growth of tree trunks. 

In carbohydrate manufacture also the light energy is used 
by the chlorophyll bodies to separate the compounds carbon 



162 RELEASE OF ENERGY IN LIVING THINGS 

dioxid (CO2) and water (H 2 0) into their elements and then 
recombine these elements (C, H, and O) to form sugar, 
which may then be changed to starch or fat. 

EXERCISE 44 

How can we determine the degrees of heat energy developed in 
the human body? Laboratory demonstration. 

Secure a clinical thermometer (111. p. 164), such as is used by a doctor 
or a nurse. Shake the thermometer to bring the mercury as low as 
possible. Wash the bulb in alcohol, and rinse in cold water. Now 
place the bulb beneath the tongue of a pupil for three minutes, or until 
the mercury ceases to rise. 

1. Describe the experiment and state the degree of heat registered 
on the thermometer. 

2. Clean and shake the thermometer as described above and repeat 
the experiment with several students. What is the average degree 
of heat in the mouths of the students tested? Compare this with the 
temperature of the room. How many degrees of heat are developed 
in the human body in this experiment? 

EXERCISE 45 

How can we show that heat energy is developed in growing seed- 
lings? Laboratory demonstration. 

Secure two wooden crayon boxes with covers or, better, two unsil- 
vered Dewar flasks (111. p. 163) or thermos bottles if they are available. 1 
Put some wet cotton batting or pieces of wet blotting paper in the 
bottom of each. Fill one of the containers two thirds full of sprouting 
peas, oats, or barley and slide in the covers or close the flasks with 
cotton. Get two thermometers that register approximately the same 
temperature, i.e. vary by only a fraction of one degree in the air of the 
laboratory. Push one thermometer through a hole in the middle of 
the cover or cotton down among the sprouting seeds, so that the bulb 
of the thermometer is covered. Through a hole in the cover of the 

1 Care should be taken to remove the sprouting grains from the Dewar flasks 
before the young plants become intertwined. 



HOW LIVING THINGS WORK 



163 



other push the bulb of the second thermometer until it is in contact 
with the wet cotton or paper. Set the boxes or flasks side by side in a 
moderately warm place for several hours. 

1. Describe the preparation of the ex- 
periment. 

2. In what respects are the conditions 
the same in both of the containers? In 
what one respect do they differ? 

3. Take the temperature readings of 
the thermometers in each and record the 
results. What difference do you notice in 
the temperature of the two ? 

4. What is your conclusion from the 
experiment as to the development of heat 
energy in the seedlings studied ? 



The degrees of heat energy re- 
leased in animals and plants. Some 
animals, like fishes, frogs, and rep- 
tiles — indeed all animals except 
birds and animals having a hairy 
covering — have a temperature that 
varies with their surroundings. 
Since animals of this sort usually 
feel cold to the touch, they are called 
cold-blooded animals. Plants too, as 
we proved by experiment, develop a 
degree of heat only slightly above 
that of their surroundings. 

Man, on the other hand, and other 
higher animals, like dogs, horses, 
and elephants, have a nearly constant 
temperature, which may be higher or 
lower than their environment. This temperature for an 
adult human being in health is approximately 98.6 degrees 




A Dewar flask 

This was invented by Sir 
James Dewar (1842-1923). 
One flask is inside the other. 
A vacuum is between them. 
A thermos bottle is similar in 
construction. 



164 RELEASE OF ENERGY IN LIVING THINGS 



rz\ 



in the mouth cavity (111. below) whether a man is traveling 
in the Arctic regions or in the tropics. Birds usually have 
a higher temperature, reaching ten degrees or 
more above that of man. 

Why food substances are a source of energy. 
When we burned sugar, starch, and fat, both 
heat and light energy became evident. Hence 
we commonly say that energy is stored up in 
these food substances, and we, therefore, call 
them fuel foods. Now how is it possible to 
have energy stored in foods ? 

A green plant is unable to manufacture sugar 
or starch without the action of light upon the 
chlorophyll bodies. Through the action of the 
radiant energy from the sun, the elements in 
carbon dioxid and water are combined and re- 
arranged to form sugar. What is the advantage 
to living things of this process carried on by the 
aid of sunlight ? 

We know that neither carbon dioxid nor 
water will burn, that is, unite with oxygen. 
The reason for this is that the carbon in carbon 
dioxid has already united with all the oxygen 
it can. Likewise the hydrogen in burning will 
unite with only enough oxygen to form water. On the other 
hand, whenever the carbohydrates are formed in the green 
parts of plants, all the oxygen in the carbon dioxid used is 
given off. So, when carbohydrates are burned, or oxidized, 
the carbon in them can unite with the same amount of 
oxygen as was given off when the carbohydrate was 
formed. 

It is during this process of union of the chemical elements 
when carbohydrates are burned that energy becomes ap- 






A clinical ther- 
mometer 

How is one's 
temperature 
taken by doc- 
tors? 



HOW LIVING THINGS WORK 



165 



parent. Hence the sun's energy is used in forming com- 
pounds (sugar and starch) that can be oxidized, or burned, 
from compounds (carbon dioxid and water) that cannot be 
burned. Sugar is essential for the making of starch, fats, 
and proteins. Since each of these food substances likewise 
can be burned, it is evident that they too, like sugar, possess 
the ability to combine with an additional supply of oxygen, 
and can " release" 
energy when they 
are burned. 

Why fuels are a 
source of energy. 
When wood, coal, 
oil, or gas is burned, 
heat and light are 
set free. Hence 
these fuels must 
have the ability to 
combine with oxy- 
gen and release en- 
ergy. Wood is made 
by plants from sugar 
just as much as are 
fats and proteins. 
So too coal, petro- 
leum, and gas are 
products formed 
from the plants (see 
111.) or from animals that lived in ages gone by and were 
all originally derived from the sugar made by plants through 
the help of the sun's rays. Thus we see that the sun is the 
ultimate source of all the energy present in foods and 
fuels. 




Coal miners at work 

The lamps on their caps were invented by Sir Humphry 

Davy. 



166 RELEASE OF ENERGY IN LIVING THINGS 






How energy is released from foods and from fuels. Our 

experiments in burning foods and common experience in 
burning fuels show us that air is necessary for this process. 
The carbon of the food or fuel combines with the oxygen of 
the air, forming carbon dioxid, and heat and light are re- 



Energy from the sun 

l!'ifor\\\$ 

photosynthesis 







Release of energy 

by 
respiration 

Foods 
conta/n/'ng 

Cand/l \ 
Any ceil 
Storage and release of energy in living things 
How is energy secured by (a) cells that contain chlorophyll? (b) by cells without 

chlorophyll ? 

leased. In our experiment with pure oxygen we found that 
this gas caused the rapid burning of the hot carbon ; we 
proved that carbon dioxid was formed and that, when 
the oxygen was used up, the light went out. Therefore, 
oxygen causes the burning and the consequent release of 
energy. 



HOW LIVING THINGS WORK 167 

EXERCISE 46 

Do pea seeds need air in order to release energy for growth ? Lab- 
oratory demonstration. 

Secure two wide-mouthed bottles and place in the bottom of each a 
wet sponge or some wet blotting paper. Pour into each bottle just 
enough water to cover the sponge or paper. Fill both bottles with pea 
seeds (or other seeds) that have been soaked in water twenty-four 
hours. Insert a tight-fitting cork into the mouth of one bottle to 
exclude the air. Leave the other bottle open to the air and add enough 
water from day to day to make up for the loss by evaporation. Put 
both bottles in a moderately warm place. 

1. Describe this experiment, showing in what respects conditions 
are the same for both groups of seeds. 

2. In what respects do the conditions differ? 

3. At the end of several days examine both bottles of seeds and 
state your observations concerning the amount of growth of the seeds 
in each bottle. 

4. State clearly your conclusions as to the necessity of air for the 
release of energy for the growth of pea seedlings. 

How we can determine whether or not oxidation takes 
place in living things. We know that sugars, starches, 
fats, and proteins are in such a form that oxygen can 
unite with them, when they are heated, and energy can be 
released from them. What process, therefore, goes on in 
plants and man that results in the release of various forms 
of energy ? Can we give further proof that oxidation takes 
place inside living things as it does outside? Since all 
these food substances contain carbon and since oxidation 
of any substance containing carbon results in the forma- 
tion of carbon dioxid, we have a sure method of determining 
whether or not the oxidation of carbon takes place in living 
things. We must find out whether the percentage of carbon 
dioxid in the air coming from the living thing or around the 
living thing has been increased. 



168 RELEASE OF ENERGY IN LIVING THINGS 

EXERCISE 47 

Does the human body form and give off carbon dioxid ? Laboratory 
demonstration. 

Breathe out through a glass tube into a test tube partly filled with 
limewater. 

1. Describe what is done and state the result. 

2. How many breaths are necessary in order to produce this result? 

3. How long was it necessary to pump air through limewater in 
order to bring about a similar result in Exercise 21 ? 

4. What proof have you from 2 and 3 that carbon dioxid is formed 
in the body? 

EXERCISE 48 

Do sprouting oats, barley, or pea seeds form and give off carbon 
dioxid? Laboratory demonstration. 

Into the bottom of each of two glass jars that can be sealed (e.g. 
quart fruit jars) place some moist blotting paper, and at one side in 
each jar put a small wide-mouthed bottle of clear limewater. Into 
one of the jars place a quantity of actively sprouting oats, barley, or 
pea seeds, sufficient nearly to reach the top of the bottle of limewater. 
Seal both jars and put them side by side in a moderately warm place 
for an hour or two. 

1. Describe the difference in the appearance of the limewater in 
the two jars. The air of which jar, therefore, contains a higher per- 
centage of carbon dioxid? 

2. What is your final conclusion? 

Respiration and the release of energy in living things. 

Our experiments have shown that living things use oxygen, 
that they form and give off carbon dioxid, and that energy is 
released. These processes are similar in all living things — 
plant, animal, and man. The release of energy from fuels 
and in living things is accomplished by an oxidizing process. 
This process necessitates the use of oxygen, and there is a 
consequent formation of carbon dioxid. Therefore, the 
release of energy resulting from the burning of fuels and 






HOW LIVING THINGS WORK 



169 



that from the oxidation of foods in living things are similar. 
The whole series of processes, including the taking in of 
oxygen, the combining of oxygen with the elements in the 
food materials (oxidation), the consequent release of energy, 
and the formation of carbon dioxid, is known as respiration. 
The essential part of the whole series of processes, however, is 
the release of some form of energy by oxidation of food substances. 

Comparison of Carbohydrate Manufacture (Photosynthesis) in 
Plants and Resfiration in All Living Things 





Carbohydrate 
Manufacture 


Respiration 
(including 
oxidation) 


Where carried on 


In green parts of plants 


In all living cells 


When carried on 


In sunlight 


Throughout life 


Substance taken from the air . . 


Carbon dioxid 


Oxygen 


Substance formed in the plant . . 


Sugar 


Carbon dioxid 


Waste substance excreted to air 


Oxygen 


Carbon dioxid 


Advantage to living things . . . 


Manufacture of food, 


Release of 




thus storing up en- 


energy 




ergy for plants, ani- 






mals, and man 





QUESTIONS AND APPLICATIONS 

1. What is meant by work ? What are some examples of work ? 

2. Define energy and name four forms of energy. 

3. Show how any one of these forms of energy may be transferred into 
another. 

4. How can you tell when work is being done? How can you tell when 
heat, light, or electricity is doing work? 

5. What observations did you make that proved (a) that certain mem- 
bers of the class develop heat energy? (b) that sprouting seeds develop 
heat energy? 

6. To what extent is heat energy released in plants? In animals? 
In man? 



170 RELEASE OF ENERGY IN LIVING THINGS 

7. Why would it be difficult to prove that a fish releases heat energy? 

8. What is the source of heat and mechanical energy in lifeless things ? 
What is the source of energy in living things ? 

9. From what source are all the forms of energy named above finally 
derived ? How does energy from its original source come to be in fuels ? 

10. How do food substances come to be a source of energy? 

11. State the observations you made that prove that certain seeds, even 
though kept moist and warm, cannot release energy for growth without air. 

12. What observations did you make that prove (a) that sprouting 
seeds form and give off carbon dioxid ? (6) That the human body forms 
and gives off carbon dioxid ? 

13. How is energy released in fuels? How is energy released in living 
things ? 

14. Name two uses of food substances. State which of the groups of 
food substances is used for each purpose. 

15. Define respiration. State the most important part of this process 
to living things. Why is oxygen essential in this process? Why are car- 
bon dioxid and water always formed when respiration goes on ? 

16. Compare the processes of photosynthesis in green plants and res- 
piration in all living things. 

17. Find out why the Davy lamp (p. 165) is of practical importance 
in mining coal. 

18. Why is each blade in the radiometer (p. 158) black on one side 
and silver color on the other ? 

19. What is the use of the vacuum in thermos bottles (p. 163) ? 

PROBLEM 2. HOW IS BREATHING CARRIED ON IN 

MAN? 

Adaptations for Breathing in Man 

Breathing and respiration compared. The essential part 
of respiration, namely, the oxidation of food substances and 
the consequent release of energy, is common to all living 
things. But the means by which the necessary oxygen is 
obtained and the waste carbon dioxid eliminated vary greatly 
in different forms of plants and animals. This part of the 
process of respiration, namely, the taking in of oxygen 



BREATHING IN MAN 171 

and the excretion of carbon dioxid, is commonly known as 
breathing. 

Breathing in man involves two distinct processes : first, 
that of taking into the lungs new supplies of fresh air, and 
secondly, that of removing from the lungs the air containing 
an excess of carbon dioxid. To the first process is given 
the name inspiration (Latin, in = into + spirare = to 
breathe) ; the second is called expiration (Latin, ex = out 
+ spirare = to breathe). 

How breathing is accomplished in man. The breathing 
organs of man are known as lungs. A lung is a structure 
having from one to a great many thin-walled elastic sacs. 
Air enters these sacs by means of elastic tubes. In the 
walls of the sacs are capillaries to absorb oxygen and give 
off carbon dioxid. Lungs are inside the body, thus the 
surfaces for absorbing oxygen can be kept moist, since 
osmosis of gases occurs readily only through moist mem- 
branes. Special means of getting air into and out of the 
lungs are necessary, and the processes by which this ex- 
change of air is accomplished are known as inhaling and 
exhaling (pp. 176-177). 

Course taken by air in man in order to reach the lungs. 
The most important organs that have to do with our breath- 
ing are the lungs. They are located within the chest cavity 
and have no immediate contact with the outside air ; hence 
there must be air passages leading to the lungs (111. p. 173). 

In ordinary breathing air enters the body through the two 
nostrils (the left one is shown in 111. p. 172). It then passes 
through the two nasal passages into the throat cavity. In 
the lower region of the throat is the slitlike glottis opening, 
through which the air enters the larynx, or voice box. This 
organ, commonly known as " Adam's apple/' projects some- 
what on the front of the neck. 



172 RELEASE OF ENERGY IN LIVING THINGS 



Below the larynx is the continuation of the windpipe, 
which, just above the level of the heart, divides into two 
main branches (111. p. 173). One of these branches supplies 
air to the right lung, the other to the left lung. Within the 
lungs these tubes branch off into a vast number of very 
small pipes called the bronchial tubes. The tiniest divisions 



Adenoid --^ 

Opening of 
eustachian tube - 

Tonsil 



Cavity for 
spinal cord 



Vertebrae *-- 




— Brain cavity 
^** Sinus cavities 
^ Nose cavity 

— Nostril opening 
— Food mass 

Epiglottis (open) 

*"- Throat cavity 



Voice box (larynx) 
Windpipe 
A lengthwise section of the head and neck 
Name the parts through which air passes from the nostrils to the windpipe. 






of these tubes open into extremely thin air sacs. Let us 
now consider somewhat in detail each of these various air 
passages. 

How the nasal passages are fitted for breathing. The 
openings into the nasal passages are guarded by numerous 
projecting hairs, by means of which a considerable amount 
of dust is kept from entering the body. The nasal passages, 
moreover, are lined throughout with mucous membrane. 
The mucus secreted by the mucous membrane catches most 



BREATHING IN MAN 



173 



of the dust and germs that have passed the hairs, unless the 
amount of these foreign substances is excessive. 

The incoming air absorbs a considerable quantity of water 
from the mucous secretion in the nose, and in cold weather 
the air is warmed by the blood in the capillaries that run 
beneath the mucous 



Thyroid car\ 
Cricoid cartilage — 

Bronchi 

Bronchial 
tubes^ 



Larynx 

—Windpipe or 
trachea 




membrane. The air, 
thus cleaned and 
warmed and mois- 
tened, enters the 
throat cavity. 

How the throat and 
the larynx are fitted 
for breathing. Ex- 
cept when something 
is being swallowed, 
the glottis is always 
open, thus allowing a 
free passage for the 
air from the throat 
through the larynx 
into the windpipe. 
When food is being 
swallowed (111. p. 
172), it is, of course, 
important that the windpipe be closed. This is accomplished 
by a little trapdoor called the epiglottis (111. pp. 97 and 172). 
If one puts the finger on the larynx region of the neck and 
then swallows, one can feel this organ rising to meet the epi- 
glottis. Within the voice box are two thin membranes called 
vocal cords that may be set in vibration by the inspired or 
expired air. These vocal cords help to produce the various 
tones of the voice. 



Air passages in the neck and lungs 

What structures not shown above are at the end of 

the smallest bronchial tubes ? 



174 RELEASE OF ENERGY IN LIVING THINGS 



Cilia 

Mucous — 
cell 

Cytoplasm- 
Cell *&— 
nuclei 



Cells lining the air passages 

What parts of these cells help to 
expel foreign matter ? 




How the lining of the air passages is adapted for filtering 

the air. The mucous lining of the windpipe and its branches 

is especially interesting. The cells 
that cover these passageways have 
on their exposed surfaces minute 
projections of protoplasm, called 
cilia (sil'i-d) (111. at left). These 
wave upward with a quick move- 
ment toward the throat and then 
more slowly recover their former 
positions. In this way any dust 
particles or germs that have 
passed the barrier of hairs at the 
nostril openings and the mucus 

secreted by the membrane of the nasal passages are moved 

steadily outward until they reach a point where they can be 

coughed out into the mouth cavity. 
How the lungs are fitted for breathing. When the finest 

branches of the bronchial tubes are traced outward from the 

windpipe, we find that each ends in a 

branching air sac with extremely thin 

walls of elastic tissue (111. at right) . As 

air comes into these sacs, they are ex- 
panded ; but as expiration begins, their 

elastic walls help to force outward 

through the bronchial tubes and the 

branches of the windpipe the air that 

has been taken into the lungs. 

The artery supplying the lungs, as 

we learned on page 118, arises from the 

right ventricle and soon divides into 

two branches, one for the right lung and one for the left lung. 

Within the lung tissue each artery divides into small branches 



Outside surface 
of lung 




Branches 
of the 
air sac 



Air tube 

Two air sacs at the end of 
a bronchial tube 






BREATHING IN MAN 175 

that follow the course of the bronchial tubes to the air sacs. 
Here the arteries communicate with a maze of capillaries, 
which run in the thin lining of the air sacs. It is here that the 
exchanges take place between the blood, the lymph, and the 
inhaled air, for these liquids and gases are separated only by 
the extremely thin walls of the air sacs and of the capillaries. 
From the capillaries of the lungs the blood finally enters 
the four veins that convey it to the left auricle. 

Changes that take place in the color of the blood after it is 
mixed with oxygen. When the blood passes through the 
lungs, it absorbs oxygen. The resulting change in color 
may be seen by the following experiment. Pour into a glass 
bottle a few spoonfuls of blood of beef that has been pre- 
vented from clotting by being stirred vigorously, with a 
bunch of twigs, and stopper tightly. When the bottle is 
shaken violently, the blood is mixed with the oxygen in the 
bottle, and the dark maroon color changes almost instantly 
to a bright scarlet. You doubtless will have observed that 
the blood in the veins on the back of the hand appears to be 
blue. But whenever blood flows from any of the veins in 
the case of a cut, the color is always bright red, after the 
blood comes in contact with the oxygen of the air. 

EXERCISE 49 

To determine the amount of enlargement of one's chest cavity 
during inspiration. Home experiment. 

Force the air out of the lungs as completely as possible. Draw a 
tape or cord around the chest under the armpits, keeping it reasonably 
tight, and measure the girth of the chest. 

1. State what you have done and record in inches the measurement 
thus determined. 

2. Inhale as much air as possible and again record the chest meas- 
urement as directed above. 



176 RELEASE OF ENERGY IN LIVING THINGS 



3. State the difference in the measurements thus obtained. 

4. What is your conclusion, therefore, as to the maximum amount 
of the enlargement of your chest cavity during inspiration? 

How air is taken into and given off from the lungs. The 

chest cavity is so constructed that its capacity can be con- 
siderably increased and then decreased. When we make 



Windpipe —" 



Sternum or 
Breastbone 



Diaphragm- 



Abdominal - 
Wall 




Windpipe 

-Additional air taken Lung- 
in or increase in 
the size of the chest 
cavity after expansion 

Sternum or'" 
Breastbone 

Diaphragm''' 



Abdominal 
Wall 




Inspiration Expiration 

Lengthwise sections through the chest cavity and abdomen 
In what ways do these two diagrams differ? 

the cavity smaller by forcing in the ribs and raising the 
diaphragm (111., Expiration), air is driven out through the air 
passages ; in other words, we exhale. Inhaling, or taking in 
air, on the other hand, is accomplished by increasing the size 
of the chest cavity. This cavity is made larger by moving 
the ribs outward and upward and by flattening and so 
lowering the diaphragm (111., Inspiration). The air in the 



BREATHING IN MAN 177 

cavity expands to fill the larger space and so tends to 
become rarefied and the outside air is forced in to fill the 
partial vacuum. 

Hygiene of the Breathing Organs 

Effect of exercise on breathing. Not only does the heart 
beat more rapidly during exercise, but the rate of breathing 
also increases. This increase in the activity of the organs of 
circulation and of breathing is necessary in order to meet the 
demand of the muscles for more energy. The cooperation 
of these organs, fortunately for us, is entirely automatic. 
The muscles cannot do more work without more energy ; 
more energy cannot be secured without more oxygen to 
oxidize the food substances in the muscles ; more oxygen 
cannot be obtained unless the breathing organs bring more 
oxygen to the blood and unless the heart drives the blood 
more rapidly to the working tissues. All this cooperation 
of the various organs is brought about and regulated by the 
nervous system and the internal secretions (pp. 569-606). 

It might be possible, however, that our breathing and 
circulatory organs, on account of lack of use, would not be 
equal to the demands of the muscles for oxygen. Hence we 
see how necessary it is that these organs should be in such 
condition that they are ready for any emergency. Vigorous 
exercise requires deep breathing. Deep breathing uses all 
parts of the lungs and tends to keep them not only in a con- 
dition such that they may be able to take in more air when 
needed, but also to resist disease more successfully. 

Since the effects of deep breathing made necessary by 
vigorous work or play are so beneficial, it has been thought 
by many people that deep-breathing exercises alone would be 
desirable. Such exercises, however, are not advisable. 
Since forced breathing when very long continued has been 



178 RELEASE OF ENERGY IN LIVING THINGS 

found to be actually harmful, such exercises should be 
carried on either with great moderation or not at all. 1 

The causes and treatment of suffocation. We have 
emphasized the fact that the body must be continually 
supplied with oxygen and that the wastes produced by 
oxidation must be constantly removed. If this process 
is interrupted, even for five minutes, fatal results are al- 
most sure to follow. If, in swallowing, food gets past the 
epiglottis into the windpipe, the air is shut off and choking 
results. In cases of this kind the head should be held for- 
ward (or downward in the case of a child), and sharp blows, 
with open hand, struck between the shoulders. 

Suffocation is some interference with the process of breath- 
ing. It may result from a blocking up of the windpipe as 
in choking, from inclosure in a small space with a limited 
supply of oxygen, from immersion in water (drowning), or 
from inhaling of poisonous gases. Carbon monoxid, for 
example, is a dangerous compound formed by the incom- 
plete oxidation of carbon. This gas is given off through 
the exhaust pipe at the back of an automobile whenever 
the engine is running. Since it is extremely poisonous and 
has no warning odor, the doors of a garage should always 
be left wide open as soon as the engine is started. 

In case of suffocation, the patient should be brought out 
at once into fresh air and a physician should be summoned. 
If the subject is unconscious but breathing, treatment for 
fainting and shock is required as follows. The feet should 
be raised and the head left low. Apply aromatic spirits of 
ammonia to the nose. Rub the legs and arms toward the 
heart to quicken the circulation. If, however, breathing 
has ceased, artificial respiration should be attempted at 
once. 

1 See Stiles, Human Physiology, p. 301. 



BREATHING IN MAN 179 

In case of drowning, do not waste time trying to get the 
harmless water out of the stomach. Lay the victim face 
downward on a flat surface or with the head slightly down- 
hill. Turn his head to one side, extend one of his arms 
above his head, and place the hand of the other under his 
face with his finger tips under his mouth to protect both 
the mouth and nose from dirt. Kneel astride one or both 
of his legs just above the knees. (1) Place your hands on 
the lower back of the victim so that your hands are about a 
palm's breadth apart, and so that the fingers and thumbs 
are resting in a natural position around the waist. 
(2) Swing the weight of your body forward on stiff arms 
until your shoulders are directly over your hands. This 
movement forces up the subject's diaphragm and causes 
bad air to be expelled from his lungs (111. p. 180). (3) Now 
remove your hands from the subject's body with a sideward 
motion and swing back to your first position (111. p. 181). 
This movement allows the victim's diaphragm to drop and 
fresh air to rush into his lungs, thus completing one respira- 
tory cycle. 

The operator rests for two seconds, then he repeats the 
artificial breathing cycle. Since each step described above 
takes one second, the first three steps, plus the two seconds 
of rest, make the total five seconds. This gives twelve res- 
pirations a minute. This is fast enough and will allow the 
operator to continue for some time with the least exhaus- 
tion. If, however, it becomes necessary for some one to 
relieve you, be sure that it is done without a break, and see 
that your successor uses the same timing that you have, 
without losing the rhythm. 1 

1 These movements of artificial respiration should be practiced by each student 
either in the class or at home, using a watch to make sure that the proper time is 
given to each part of the treatment. This practice may later in life result in the 
actual saving of lives. 



180 RELEASE OF ENERGY IN LIVING THINGS 

To assist in properly timing these movements, repeat 
either silently or aloud during the period of pressure " out 
goes the bad air " and during the period of release " in comes 
the good/' or count slowly, " one, two, three " for pressure 
and " four, five " for release, one count for each second. 

Cases have been reported of persons who have been under 
water as long as thirty minutes and yet have been resus- 




Courtesy of Captain Charles B. Scully 

Artificial respiration (Schaefer method) 

Forcing the air out of the lungs (exhaling) . Captain Scully (left) has saved 377 persons 

from drowning and was awarded the Congressional Medal in 1926. 

citated after five and one half hours of continuous work. 
There is no certain sign by which the layman can determine 
that it is too late for artificial respiration. Efforts should 
not be abandoned for at least two hours. 

How the composition of the air is kept nearly the same 
from year to year. All living things are using up the oxygen 
of the air in order to release the energy of the food stored in 
the cells and are giving off carbon dioxid to the air. The 



BREATHING IN MAN 



181 



burning of wood, coal, gas, and other fuels all over the world 
likewise results in depleting the oxygen of the air and in the 
addition of large quantities of carbon dioxid. Hence it 
would seem that the air would eventually become so charged 
with carbon dioxid and become so lacking in oxygen that 
life on the earth would finally cease to be possible. Analyses 
of outdoor air of city and country, however, in various parts 




^ t >A^^6>Qt^Q^_ 



Courtesy of Captain Charles B. Scully 

Artificial respiration (Schaefer method) 
Allowing the lungs to fill with air (inhaling) . 

of the world show that the relative amounts of oxygen and 
carbon dioxid in the air vary but little. How can this be 
explained ? 

Green plants, when exposed to light, take the carbon dioxid 
from the air in the process of sugar manufacture ; but since 
only the carbon of the carbon dioxid is needed, the excess 
oxygen is returned to the air. The plant, of course, all the 
time needs oxygen to bring about the release of energy ; but 
in the light the plants give off much more of this gas than 



182 RELEASE OF ENERGY IN LIVING THINGS 

they can use in respiration. This oxygen is set free into the 
atmosphere by land plants and into the water by plants 
living under water. Hence we see why it is possible to keep 
an aquarium running for a long time without changing the 











Pill:.' 1 : 


;.,,.* 


: 


w-l: ^■■■u-s . v. ... 




■ s - : : : : -- -i>* : ^- :■■ 


Jij€ii;JI||| 










" : ^Wt'- : V:^5: 






*-: '# 




%.~" 






\gL j« *JfffLy 


fr-y- 


ypylt2|y:y,yy.; 




^SffHHHl 




' J 






* 




.. .:" 




9f\ . 



An aquarium 

What gas needed by the plants is supplied by tadpoles ? With what gas do the green 

plants supply the tadpoles ? 

water if the exchange of gases of the animals and plants is 
properly balanced (111. above). 

The beneficent activities of green plants all over the 
globe, together with the constant mixing of the atmosphere 
due to the world-wide action of winds, will help us to under- 
stand how the air is kept so nearly in a constant condition 
as regards the relative amounts of oxygen and carbon di- 
oxid. The processes by which the carbon of the carbon 
dioxid is made a part of foods and fuels by plants and then 
in turn is given back to the atmosphere as carbon dioxid 



BREATHING IN MAN 



183 



by the respiration of both plants and animals comprise 
what is known as the carbon cycle (111. below). 

How the condition of the air is kept suitable for breath- 
ing. In inclosed spaces, such as living rooms or the rooms 
where people congregate — halls, churches, theaters, and 
schools — where the air is prevented from free movement 
and from mixing with the outer atmosphere, the air soon 







Assimiiation of 
^ fe. food substances to 
form pro top /a sm ' 
ofan/ma/s * 
Oxidation of food 
substances in 
animais ¥ 
Food substances 
eaten by an/ma/s, * 

Ass/m/'/at/on of 
food substances^~^ m ^^^g a 
'to form protop/asm 
of green p/ant """ "*"»p 
Oxidation of 
food substances 




Death of 
animai 



^^in green piants ^^^ 
to reiease energg^\ 



JForm ed into 
carbohgdrateSi 
fats and protein 



X 



Taken into 
green piants 





Decag of 
animai due 
to bacteria 



CO± 
fn the oir^ 

The carbon cycle 
Beginning with CO2 in the air in each of the five cycles as follows : 

1. Name the various steps in carbon cycle 1 through the green plant until CO2 is 
returned to the air. 

2. In the same way trace carbon cycle 2 until the decay of the green plant returns 
the CO2 to the air. 

3. Trace carbon cycle 3 which has to do with the formation and oxidation of fuels. 

4. Show by tracing out carbon cycle 4 how energy is released in animals and CO2 
returned to air. 

5. Follow carbon cycle 5 from the CO2 in air through the life and death of an 
animal. 

* This is equally true of plants without chlorophyll. 



184 RELEASE OF ENERGY IN LIVING THINGS 

becomes stuffy, and the occupants suffer discomfort, which 
increases with the number of people. This, if carried to an 
extreme, would result in the death of the occupants of such 
a room. Since no living thing can exist in an atmosphere 
consisting to any considerable extent of carbon dioxid, it has 
been thought that carbon dioxid given off from living things 
is the principal cause of the discomfort arising from stale air 
and, in extreme cases, of the death of the people or of the 
animals subjected to such air. 

It is, of course, true that no animal or plant can live in 
pure carbon dioxid, since carbon dioxid does not support 
oxidation. But neither does nitrogen support burning, and 
death will result likewise in an atmosphere of nitrogen alone. 
It likewise has been thought that there are unknown poison- 
ous substances exhaled by the body that render the air 
harmful. But of this there has yet been no proof. 

Why, then, does air become unsuitable for breathing 
in rooms where people congregate? Every one knows that 
when the air becomes heated beyond a certain point, it is 
not agreeable ; and if at the same time the air is charged with 
moisture to a considerable extent and so becomes humid, 
one feels discomfort, whether in an inclosed room or out of 
doors. If, in addition to these two atmospheric conditions, 
the air remains undisturbed, it becomes very disagreeable. 
We have all experienced such conditions out of doors as 
well as in rooms that are poorly ventilated. 

Now certainly, in the case of out-of-doors air, the dis- 
comfort could not be due to carbon dioxid or to the so-called 
poisonous substances that may be present in close rooms. 
To prove that carbon dioxid had very little to do with 
making air, uncomfortable or harmful for breathing, experi- 
ments like the following were tried : A number of persons 
were kept in a chamber in which the composition of the air 






BREATHING IN MAN 



185 



could be controlled. When such air was kept free from car- 
bon dioxid but was allowed to become warm and moist, 
the persons suffered great discomfort and were unable to 
carry on work effectively. When, on the other hand, the 
carbon dioxid was not removed, but the air was kept cool, 






\\ 



K\/~o 



utlet 

through roof 



CeYY/ng 



Outlet for 
bad air 



■ 



Thermometer 
near desk 



68*F 



Window 
open 



Deflector 



Radiator 



F/oor Y/ne 



Courtesy of National Tuberculosis Association 

A diagram to show good methods of ventilation 
Where does air enter the room? How is the deflector useful? 

the excess moisture removed, and the air kept in motion, 
those experimented upon felt perfectly comfortable and were 
able to do good work, and no ill effects from the excess of 
the carbon dioxid were apparent, unless the waste gas was 
allowed to increase to a degree far beyond that experienced 
under ordinary living conditions. 



186 RELEASE OF ENERGY IN LIVING THINGS 

Evidently, then, that air of inhabited rooms may be 
suitable for breathing, it is necessary to change the air in 
such a way as to keep it cooled and moistened to an agree- 
able extent and also to give it gentle movement. Now air 
from the great outdoors more nearly provides such condi- 
tions ; hence we open the windows of our rooms to furnish 
the interchange of fresh air outside with the warmer, moister, 
and more quiet air inside and not necessarily to get rid of the 
carbon dioxid. It is possible by artificial means so to venti- 
late rooms that the air at all times, without regard to the con- 
ditions of the outer air, shall be agreeable on account of being 
of suitable temperature, of suitable degree of moisture, and in 
gentle motion. A window over a radiator, opened top and 
bottom (p. 185), will provide for the warming of the in- 
coming air and will give suitable ventilation, especially if a 
transom is open at the other side of the room. 

QUESTIONS AND APPLICATIONS 

In your notebook number lines 1-25. Supply the missing word or words 
wherever necessary, or choose the word or words that are in italics which 
will make the given statements true. 

Air sacs are at the end of the smallest (1). The walls of air sacs are 
fitted for interchange of gases because they are (2), and because they con- 
tain blood vessels called (3). In all the air passages, incoming cold air is 
warmed by the (4), and dry air is moistened by the (5), and dusty air is 
filtered by (6). Cilia in the windpipe move more rapidly (inward) (out- 
ward) (7). To help exhale, the diaphragm becomes (more) (less) dome- 
shaped (8). To inhale, the ribs and breastbone move (outward and up- 
ward) (downward and inward) (9) . (Air rushes in first and so enlarges the 
chest) (the chest enlarges first and then the air rushes in) (10). Deep breath- 
ing without exercise when continued for several minutes is (harmful) 
(beneficial) (11). The air in living rooms in cold weather is usually 
(too warm) (too cold) (12), (too quiet) (too breezy) (13), (too dry) (too moist) 
(14). The air in living rooms in the winter will be much improved for 
breathing purposes if a window is opened a little, because the air will be 






BREATHING IN MAN 187 

(15), and (16), while in a third respect the air will be only a little improved 
because it will become just a little (17). Green plants supply animals with 
food and (18), and animals supply plants with fertilizer and (19). Green 
plants during the warm seasons give off more (20) than they use, and take 
in more (21) than they give off. When one swallows, the windpipe open- 
ing, known as the (22), is closed by the (23). If a person has been suffo- 
cated by immersion in water or by inhaling poisonous gases, if unconscious 
but still breathing he should be treated for fainting and (24). If breathing 
has ceased, (25) should be attempted at once. 

Find answers to the following questions : 

1. Why does the air in heated rooms in winter tend to become rela- 
tively drier as the temperature of the air outside becomes colder? 

2. Find out if you can why it is that one is so much more uncomfortable 
when the air is very warm, and very humid than when the air is very warm 
and dry. 

3. Why does one feel cooler in very warm air when a current caused by 
an electric fan passes over one's body? 

4. Look up an account of the " Black Hole of Calcutta," and see if you 
can account for the death overnight of 123 out of 146 of those British 
prisoners. 



UNIT VI. WHAT WE SHOULD EAT AND WHY 

Why many people without any scientific knowledge of diet 
are healthy and vigorous. Undoubtedly there are many 
scientific truths that seem to have no direct relation to 
human welfare. If this were true of scientific knowledge 
concerning the diet, the discussion that is to follow might 
well be omitted from a high-school biology. But such is 
not the case. 

We all know that, when one is ill, special attention must 
be given to the nature, the preparation, and the amount 
of food that is eaten. Is this true likewise if one wishes to 
keep in a state of health ? There is no doubt that there are 
many people who know very little about the reasons for 
eating certain kinds of food or about the relative value of 
different foods, and yet they are vigorous, healthy, and 
happy. A careful study of the diet of such people will show 
that they are actually getting the kinds of food and about 
the quantity of each food substance needed to keep their 
bodies in a state of health. In other words, they are doing 
the right thing without knowing why. They are following 
in most cases food choices learned from their parents. Now 
this knowledge gained through experience probably serves 
us well as long as we continue to eat the same kinds of foods 
and in the same way. 

Why a knowledge of food values and of diet is important. 
But suppose it is difficult to get the accustomed food either 
through lack of money or because foods sold under the same 
name have a different composition. In order to economize, 
for instance, families often use less milk than formerly, 

188 



WHAT WE SHOULD EAT AND WHY 189 

evidently regarding this food as a luxury. In fact there is 
an unfortunate tendency to decrease the amount of milk 
used on account of its increased cost. This is poor economy, 
as we shall see. 

Again, because of the cost of butter fats, many substitutes 
for butter are used, which consist of vegetable or animal fats 
flavored to taste like butter. These " butters " can be sold 
more cheaply, and many people buy them for this reason, 
thinking that the source of the fat they eat makes no differ- 
ence. It is important to remember, however, that vegetable 
fats are poor in certain food essentials. The leafy parts of 
plants in the form of salads and greens are also often omitted 
to a considerable extent either because of lack of apprecia- 
tion of their importance or because of the high cost of such 
foods. 

Then, too, there are the numerous prepared breakfast foods 
and breads made from various grains, which, though they 
may have the same names as formerly, have not the same 
composition as when the whole of the wheat, corn, or rye 
was ground up to form flour or meal. In order to get whole 
wheat, corn, or rice in these days, one may have to pay a 
higher price for the product and make a special effort to 
get it. 

Thus for one reason or another we may change our tradi- 
tional diet without being aware that we are depriving our- 
selves of some essential food ingredient. If, however, the 
housewife knows the dangers that result from eating grains 
deprived of essential food substances and if she appreciates 
the importance of supplying plenty of milk, butter, and green 
foods, it is reasonable to suppose that she would plan the 
family diet accordingly. 

How the uses of the various food substances were deter- 
mined. It has long been known that some of the foods we 



190 WHAT WE SHOULD EAT AND WHY 

eat are in some mysterious way converted into the substance 
of our bodies, and as a consequence we grow. From foods 
and oxygen, too, we secure the necessary energy to carry on 
our daily tasks. It is only in recent times, however, that 
scientific investigations have solved many of the mysteries 
concerning the part played in the body by the different food 
substances. 

In the first place, the five distinct classes of food substances 
named on page 33 were discovered in the foods we eat. Next, 
by trying many feeding experiments on animals and man, 
scientists demonstrated the particular uses of each of these 
food substances (111. p. 198). 

What the uses of the various food substances are. As a 
result of scientific work of this sort, we find that each of the 
five classes of food substances of which all our foods consist 
can be put into one or the other of two groups : first, those 
that supply us with energy by the process of oxidation ; and, 
second, those that provide materials for building up the 
body. 

The principal food substances that act as storehouses of 
energy (the fuel foods) are the carbohydrates and fats (or 
oils) — food substances that do not seem to be used in the 
building up of protoplasm. If, however, the body is not 
supplied with a sufficient amount of these fuel foods, proteins 
may also be oxidized to furnish us with energy. Water and 
mineral matter cannot, of course, serve as fuel since they 
cannot be burned. 

For the building up of protoplasm, on the other hand, pro- 
teins are absolutely essential, since without them growth and 
repair cease and death finally results. For protoplasm build- 
ing, certain mineral compounds are also required, even though 
in small quantities. Some of the necessary elements fur- 
nished by these compounds are phosphorus, calcium, and 



WHAT WE SHOULD EAT AND WHY 191 

Table of Edible Organic Food Substances in Some Common Foods 1 



Food 



Apples 

Bacon (smoked) . . 
Bananas .... 
Beans (fresh string) . 
Beans (canned baked) 
Beef liver .... 
Beef (ribs, fat) . . 
Beef (sirloin steak) . 
Beets (cooked) . . 
Bread (white) . . . 

Butter 

Cabbage .... 
Carrots (fresh) . . 

Celery 

Cheese (American) . 
Codfish (dressed) 
Corn (fresh, sweet) . 
Cornmeal .... 

Cream 

Eggs (uncooked) . . 

Fowl 

Ham (fresh, lean) 
Lamb (leg roast) . . 

Lettuce 

Lobster 

Milk (whole) . . . 
Oatmeal .... 
Onions (fresh) . . 

Oranges 

Oysters 

Peas (green) . . . 
Pork chops (medium) 
Potatoes (white, raw) 
Sausage (Bologna) . 
Spinach (fresh) . . 
Tomatoes (fresh) . . 
Veal cutlet .... 



Percent- 


Percent- 


Percent- 


Calories 


age of 
Protein 


age of 
Fat 


Carbo- 
hydrate 


per 

Pound 2 


.4 


.5 


14.2 


285 


10.5 


64.8 





2840 


1.3 


.6 


22.0 


447 


2.3 


.3 


7.4 


184 


6.9 


2.5 


19.6 


583 


20.4 


4.5 


1.7 


584 


15.0 


35.6 





1721 


18.9 


18.5 





1099 


2.3 


.1 


7.4 


180 


9.1 


1.6 


53.3 


1199 


1.0 


85.0 





3491 


1.6 


.3 


5.6 


143- 


1.1 


.4 


9.3 


204 


1.1 


.1 


3.3 


84 


28.8 


35.9 


.3 


1990 


11.1 


.2 





209 


3.1 


1.1 


19.7 


459 


9.2 


1.9 


75.4 


1620 


2.5 


18.5 


4.5 


883 


13.4 


10.5 


— — ■ 


672 


19.3 


16.3 





1017 


25.0 


14.4 





1042 


19.7 


12.7 





876 


1.2 


.3 


2.9 


87 


16.4 


1.8 


.4 


379 


3.3 


4.0 


5.0 


314 


16.1 


7.2 


67.5 


1811 


1.6 


.3 


9.9 


220 


.8 


.2 


11.6 


233 


6.2 


1.2 


3.7 


228 


7.0 


.5 


16.9 


454 


16.6 


30.1 





1530 


2.2 


.1 


18.4 


378 


18.7 


17.6 


.3 


1061 


2.1 


.3 


3.2 


109 


.9 


.4 


3.9 


104 


20.3 


7.7 





683 



1 Selected from Chemistry of Food and Nutrition, 4th ed., by Henry C. Sherman. 
The Macmillan Company, N. Y., 1932. 2 g ee pp. 194-197. 



192 WHAT WE SHOULD EAT AND WHY 

iron. Water, too, in considerable amounts is always present 
in living protoplasm and must, therefore, be supplied in the 
diet. For making the hard parts of the teeth and the bones, 
phosphates and carbonates of lime are two of the necessary 
minerals. 

Substances that are neither fuels nor building materials 
for the manufacture of protoplasm have been discovered in 
foods. These substances are known as vitamins. Their 
functions are concerned with the regulation of growth and 
with the healthy development of the body. 

EXERCISE 50 

How does the composition of animal foods and of vegetable foods 
differ? Homework. 

1. Arrange in one column five animal foods with the highest per- 
centage of protein (see chart p. 191), and in a parallel column five 
plant foods with the highest percentage of protein. Find the average 
percentage of protein in each case. 

2. In the same manner as in 1 above find the average percentage 
of fats in five animal foods and in five plant foods which have the 
highest percentage of fats. 

3. As above find the average percentage of carbohydrates in five 
animal foods and five plant foods having the highest percentage of 
carbohydrates. 

4. Complete the following sentence by substituting the appropriate 
words for the letters (a), (b), and (c) : Animal foods from the chart on 
the average have a higher percentage of (a) and (6), while plant foods 
have a higher percentage of (c). 

Sources of the various foods needed in the daily diet. In 

order to secure the fuel necessary to furnish the energy we 
need, we must have foods rich in fats and carbohydrates. 
As examples of foods containing a high percentage of fats, 
we may select butter, milk, bacon, olive oil, and most of the 
nuts and nut butters. As sources of carbohydrates we may 



WHAT WE SHOULD EAT AND WHY 193 

choose any of the cereal foods or the breads made from them, 
potatoes, bananas, apples, sweet corn and many other foods 
derived from plants (p. 191). 

In addition to the fuel foods we must secure for our daily 
consumption foods that will supply the proteins, mineral 
matters, and the water required for building up the body 
and keeping it in repair. A few examples of foods that have 
a fairly high percentage of proteins are the flesh of animals 
(beef, pork, mutton, fish, and fowl), eggs, beans, peas, and, 
to a certain extent, the cereals. Foods rich in mineral 
matters are the vegetable greens and salads in which the 
leaves of plants are used, whole wheat bread and whole rye 
bread, and breakfast foods made from wheat and other 
whole grains such as corn and oats. 

Lastly, the foods we eat should also contain an adequate 
percentage of the various vitamins. Such foods are the 
leafy parts of plants, fresh fruits, milk, butter fat, yolk of 
eggs, whole wheat and rice and other grains, potatoes, both 
white and sweet. 

What quantities of the various food substances are needed 
in a daily diet. Various investigators in our country and in 
Europe have determined the amounts of proteins, fats, and 
carbohydrates that healthy men on the average consume 
while engaged in different occupations. While the results 
of these studies differ in some respects, in all the averages 
the amount of carbohydrates recommended is much greater 
than that of either proteins or fats. One authority, for in- 
stance, asserts that the amount of carbohydrates for an 
adult man at moderate work should be twice as much as 
fats and proteins together and that the relative amounts of 
fats and proteins should be about equal. 

If an engine is to do a great amount of work, it must be 
large enough and strong enough for the given purpose and 



194 WHAT WE SHOULD EAT AND WHY 



>Electric wires 
for setting 
fire to food 



— %—§-Water 



must be supplied with sufficient fuel to furnish the necessary 
energy. A man who does strenuous muscular work needs 

enough proteins, 
water, and mineral 
matter in his diet to 
keep his tissues in 
good condition and a 
generous supply of 
fats and carbohy- 
drates to act as fuel. 
The clerk, the book- 
keeper, or the stu- 
dent, however, needs 
considerably less of 
the fuel foods. 

What Calories are. 
You may have heard 
some one who wished 
to weigh less say : 
" I must eat fewer 
Calories." Now, of 
course, one cannot 
really eat Calories, 
since, as you will 
presently under- 
stand, a Calorie is 
not a food, though it 
is closely associated 
with foods. A Calorie is the amount of heat necessary to raise 
the temperature of four pounds of water one degree Fahrenheit. 1 

1 More exactly, a Calorie is defined as the amount of heat necessary to raise the 
temperature of one kilogram of water one degree Centigrade. This is the great 
Calorie. The small calorie is the amount of heat necessary to raise one gram of 
water one degree Centigrade. 







vAir casings 
to prevent 
loss of heat 

|p Oxygen 

-Thermometer 

~ | ~Food sample 



From Sherman's "Chemistry of Foods and Nutrition" 

A bomb calorimeter 

Where is the food sample placed? How is the 
food caused to burn? How is the fuel value de- 
termined ? 






WHAT WE SHOULD EAT AND WHY 195 

You already know that when fuels are burned or oxidized, 
heat is released. This is also true of foods. If a given 
amount of food or of fuel when burned raises the temper- 
ature of four pounds of water 100 degrees Fahrenheit, we 
say that the food or fuel released 100 Calories of heat. 
Since carbohydrates, fats, and proteins may all be burned, it 
is possible to determine the number of Calories that a given 
amount of each food will yield. The apparatus used to de- 
termine the number of Calories a given amount of food or 
fuel will yield when burned is known as a calorimeter (kal'- 
o-rfm'e-ter) (111. p. 194). The following table shows the 
number of Calories that one ounce of a fuel and one ounce 
of each of the three food substances will yield when oxidized 
in the calorimeter. 

1 ounce of coal will yield approximately 166 Calories. 

1 ounce of carbohydrates will yield approximately 120 
Calories. 

1 ounce of proteins will yield approximately 120 Cal- 
ories. 

1 ounce of fat will yield approximately 275 Calories. 

When a food is oxidized in the human body, the number of 
Calories released is somewhat less than when the same 
amount of food is burned outside the body. This fact is 
taken into account in the tables that show the number of 
Calories yielded by given weights of various foods when they 
are oxidized in the human body. The table on page 196 
shows 100-Calorie portions of some of the common foods. 

You will now understand why we may speak of eating so 
many Calories of butter, sugar, potatoes, or of any other 
food. If more Calories are eaten than can be burned in the 
body for the release of heat and other forms of energy, or 
for the repair or building up of the tissues, the excess must 



196 WHAT WE SHOULD EAT AND WHY 

100-Calorie Portions of Some of the Common Foods 1 



Food 



Bread, white . . 

Oats, rolled . . . 
j Banana .... 
\ Orange 

Beans, baked, canned 

Cabbage .... 

Lettuce .... 

Peas, canned . . . 

Potatoes, white . . 

Tomatoes, fresh 
[ Butter 

Egg yolk .... 
[ Milk, whole . . . 
( Beef, rib roast . . 
j Chicken, broiled 
j Lamb chops . . •'. 
1 Salmon, canned . . 
Walnuts, English, shelled 
Sugar, brown . . . . 



Weight 
in Ounces 



1.3 
1 

5.5 

9.5 

2.7 

11.2 

18.5 

4.4 

5.3 

15.5 

.5 

1 

5.1 
1.6 
2.6 
1.6 
1.8 
.5 
.9 



Approximate Measure 



2 slices, 2\ in. X 2f in. 

i cup 

1 large banana 

1 large orange 

1 cup 

5 cups, shredded 

2 large heads 
f cup 

1 medium white potato 
2-3 medium tomatoes 

1 tablespoonful, scant 

2 yolks 



Slice, 5 in. X 
Slice 4 in. X 

1 chop, 2 in. 
\ cup 

8-16 nuts 

2 tablespoonfuls 



X iin. 

i 



z-j in 

2\ in. X i in 

X 2 in. X I i 



either be eliminated as waste or stored in the tissues as fat. 
When overindulgence in food is continued, the person be- 
comes overweight, and the excess of fat becomes not only 
burdensome, but also, in the case of adults, dangerous. One 
is overweight or underweight when one's weight is very 
much more or very much less than the average for one's 
height and age. If you are more than 15 per cent above 
the average, you should eat fewer Calories. If you are more 
than 7 per cent below the average, you should eat more 
Calories. The danger of overweight applies quite largely to 
adults and underweight to growing boys and girls. To de- 

1 Selected from Willard and Gillett, Dietetics for High Schools, Rev. ed., The Mac- 
millan Company, 1930. 



WHAT WE SHOULD EAT AND WHY 197 

termine whether you are overweight or underweight you 
should consult the tables in textbooks on dietetics. 1 

The following table shows the Calorie requirements per 
day for boys and girls. You should, of course, remember that 
not all your dietary needs can be measured in Calories. The 
minerals, vitamins, water, and roughage so essential for 
health must also be included. Likewise the proper propor- 
tion of Calories of protein must also be secured if growth 
and repair are to be made possible. 

Table of Food Allowances for Children 2 



Age in 


Calories 


per Day 


Age in 
Years 


Calories 


per Day 


Years 


Boys 


Girls 


Boys 


Girls 


Under 2 


900-1200 


900-1200 


9-10 


1700-2000 


1550-1850 


2-3 


1000-1300 


980-1280 


10-11 


1900-2200 


1650-1950 


3-4 


1100-1400 


1060-1360 


11-12 


2100-2400 


1750-2050 


4-5 


1200-1500 


1140-1440 


12-13 


2300-2700 


1850-2150 


5-6 


1300-1600 


1220-1520 


13-14 


2500-2900 


1950-2250 


6-7 


1400-1700 


1300-1600 


14-15 


2600-3100 


2050-2350 


7-8 


1500-1800 


1380-1680 


15-16 


2700-3300 


2150-2450 


8-9 


1600-1900 


1460-1760 


16-17 


2800-4000 


2250-2600 



How protein deficiencies in our diet may be made good. 

It was formerly supposed that one kind of protein was as 
good as another and that the only matter of importance was 
to get enough proteins. The work of recent investigators, 
however, shows that the kinds of proteins eaten are as impor- 
tant as the amounts, if not more so ; for, if the right kinds are 
not eaten and in the right proportions, growth is interfered 
with or may even be stopped (111. p. 198). To supply 

1 Willard and Gillett, Dietetics for High Schools, Rev. ed., pages 9-15, The 
Macmillan Company, N. Y., 1930. 

2 Taken from Food Allowances for Healthy Children, Publication 120, Association 
for Improving the Condition of the Poor, N. Y. 



198 WHAT WE SHOULD EAT AND WHY 

possible deficiencies in the proteins we eat, milk is recom- 
mended, since it has the necessary proteins in better propor- 
tions than any other single food. 

How mineral deficiencies in our diet may be made good. 
When wheat or rice are treated in such a way as to remove 
the outer coats, as is done in polishing rice and in preparing 
wheat flour, valuable mineral matter as well as other needed 




Courtesy of Nutrition Laboratory, Battle Creek Sanitarium 

The kind of protein in milk makes a difference 
These two rats were of the same age. Both were fed the same amount of whole 
wheat cereal. The one on the left was given one teaspoonful of cream, and the one 
on the right one tablespoonful of whole milk. 

substances are removed. To make up for this loss, one 
should eat liberal quantities of the leafy parts of plants 
(e.g. spinach, lettuce, and cabbage), since they contain the 
necessary mineral matter in better proportions than the 
other parts of plants. Milk, however, is about the best 
food to furnish the calcium and phosphorus of which the 
hard parts of the teeth and bones are largely composed. 

How vitamin deficiencies in our diet may be made good. 
On page 192 we mentioned a group of substances found in 






WHAT WE SHOULD EAT AND WHY 199 



natural foods that differs in function from any of the five 
classes of food substances. These substances are called 
vitamins because of their great importance in vital, or life, 
activity. The vitamins that we shall discuss are known re- 
spectively as vitamin A, B, C, and D. 

Certain diseases of children and of adults are due to a lack 
of one or more of these vitamins in the food eaten. Scurvy, 
for instance, has long been known to be due to a deficiency 
in the diet. Anyone suffering from this disease becomes 
gradually weaker until after a time he is unable even to sit 
up, and in extreme cases death results. Sailors on long voy- 
ages formerly were subject to this disease even when they 
had plenty of substantial foods that contained sufficient 
fats, carbohydrates, and proteins if at the same time they 
were deprived of fresh fruits and vegetables. When these 
fresh foods are supplied to those who are ill with scurvy, 
their strength returns and the disease soon disappears. 
Bottle-fed babies are likely to develop scurvy when they 
drink milk which has been heated as in Pasteurization. The 
heat destroys the vitamin that prevents scurvy. This vita- 
min is known as vitamin C. The remedy here lies in giving 
a little orange juice or the juice of tomatoes, each of which 
is an excellent source of vitamin C (Table p. 204). 

Another disease due to a lack of a vitamin is an eye disease 
that may lead to blindness. This disease is due to the lack 
of a vitamin known as vitamin A found in butter fat, in 
the fat in the yolk of an egg, and also in spinach and 
carrots. Two young rats, as nearly alike as possible, were 
fed exactly the same rations except that one received no 
vitamin A and the other vitamin A present in whole milk. 
While the latter developed normally, the one without vita- 
min A was less than half the size of its mate and developed 
the eye disease. If an experiment of this type is carried too 



200 WHAT WE SHOULD EAT AND WHY 

far, blindness results. When, however, butter fat was sup- 
plied, the young animal rapidly recovered and became normal. 
This is due to vitamin A. It has been shown that carotine, 
the yellow pigment in carrots and other yellow vegetables, is 




From Mary Swartz Rose, "Teaching NWrition to Boys and Girls' 

The difference made by vitamin C 
The guinea pig in the upper picture had plenty of vitamin C supplied by orange juice. 
The guinea pig in the lower picture was fed on raisins, hence no vitamin C. Otherwise 
the food of both animals was the same. 



WHAT WE SHOULD EAT AND WHY 201 

the mother substance of vitamin A. In the liver this pig- 
ment is converted into the vitamin which is not itself yellow. 
Beriberi is a nerve disease rather common in the Orient. 
It has also occurred in Labrador and occasionally in other 
parts of the world. This disease results when polished rice 




From Mary Swartz Rose, "Teaching Nutrition to Boys and Girls" 

The difference made by vitamin A 
The upper rat was fed everything in whole wheat bread and milk except vitamin A. 
The lower rat received plenty of vitamin A from the milk in his whole wheat bread and 
milk diet. 

or white bread is used to the exclusion of fresh meat and 
fresh vegetables. The polishings from rice are found to 
contain vitamins. When these are added to the diet, the 
sufferers very soon recover. Leafy parts of plants also con- 
tain the vitamin that prevents beriberi. This vitamin is 
known as vitamin B. 



202 WHAT WE SHOULD EAT AND WHY 

Rickets is a disease of the bones of children. In this dis- 
ease the bones do not develop properly because the mineral 
compounds containing calcium and phosphorus are not made 
use of in sufficient amount to construct properly the bony 




Courtesy of Dr. Harry Sleenbock 

Animals, like children, may build a poor framework 

These dogs are of the same age. What difference do you note in the framework of 
the two dogs ? Which dog must have lacked calcium compounds and vitamin D ? 

tissues. As a result the bones become misshapen because 
they are not rigid enough to bear the weight put upon them 
(111. above). So primarily rickets is a disease due to the 
lack of sufficient calcium and phosphorus compounds in the 
blood stream to form the calcium phosphate which make 
the bones rigid. Hence, it is evident that the foods which 



WHAT WE SHOULD EAT AND WHY 203 

furnish the calcium and phosphorus should always be in- 
cluded in the diet in liberal amounts. Two foods which are 
valuable for this purpose are cows' milk and the leafy parts 
of plants. 

But it has been proved that even if the calcium and phos- 
phorus compounds are present in abundance in the foods, 
these mineral matters are not always present in the proper 




Courtesy of Dr. Harry Sleenbock 

Sunshine makes vitamin D, the " calcium helper " 

Both chickens had plenty of calcium and phosphorus from milk. The one on the 
right had plenty of sunshine. The one on the left was kept in a dark room. What 
difference does sunshine make ? 

amounts in the blood stream, and in such cases rickets will 
still occur. It has long been known that if cod-liver oil is 
added to the diet, the rickets may be cured and also pre- 
vented, but no one knew why cod-liver oil acted in this way. 
In recent years, however, it has been proved that cod-liver 
oil and other fish oils are rich in a vitamin which helps 
to prevent and cure rickets. This vitamin is known as 
vitamin D, or the anti-rachitic vitamin, or in other words 
the vitamin which prevents rickets. Cows' milk, butter, 



204 WHAT WE SHOULD EAT AND WHY 

Table of Foods as Sources of Vitamins A, B, and C 1 

x indicates that the food contains the vitamin. 

xx indicates that the food is a good source of the vitamin. 

xxx indicates that the food is an excellent source of the vitamin. 

— indicates that the food contains no appreciable amount of the vitamin. 

? indicates doubt as to the presence or relative amount. 

* indicates that evidence is lacking or appears insufficient. 



Food 



Asparagus 

Beans, navy, dry or canned 
Beans, string, cooked . . 

Beef 

Bread, white, water . . . 
Bread, whole wheat, milk . 

Butter 

Cabbage, green, raw . . . 
Cabbage, head, raw . . . 
Carrots, fresh, young . . 

Egg white 

Egg yolk ........ 

Grapefruit (or juice) . . . 

Lettuce 

Liver 

Milk, whole 

Olive oil 

Orange juice 

Peanut oil 

Peas, young, green . . . 
Potatoes, sweet .... 

Potatoes, white 

Raisins 

Rice, "polished" white . . 
Rice, whole grain .... 

Spinach, raw 

Tomatoes, raw or canned . 
Yeast 



Vitamin A 



variable 

x 

xx 

x 

? 

xx 
xxx 
xx 

X 

xxx 
xxx 

X 

x to XX 

xx to xxx 

xxx 

— to X 

XX 

? 

XX 
XX 
X 



X 

xxx 

XX 



Vitamin B 



xxx? 
xx 
xx 
xx 
x 
xx 

xx 

XX 
XX 

XX 
XX 
XX 
XX 
XX 



XX 
XX 
XX 
X 

XX 
XX 
XX 

xxx 



Vitamin C 



XX 

— to X 

— to X 

xxx 
xxx 

XX 

— ? 

_? 

XXX 

XXX 

X 

x variable 
xxx 
xxx 

XX 
XX 



xxx 
xxx 



1 Selected from Chemistry of Food and Nutrition, 4th ed., by Henry C. Sherman, 
The Macmillan Company, N. Y., 1932. 



WHAT WE SHOULD EAT AND WHY 205 

and the leafy parts of plants also contain vitamin D but 
in less proportion than cod-liver oil. 

It has been discovered that the direct rays of the sun 
shining on the skin also have the same effect as vitamin D of 
cod-liver oil in curing or preventing rickets. It seems prob- 
able that a substance which is always present in the skin is 
changed by the action of sunlight to a substance that acts 
like vitamin D. This substance is then absorbed by the 
blood the same as vitamin D and causes the phosphorus and 
calcium compounds if present in the body to appear in the 
blood stream, thus preventing and curing rickets. 

Hence it must be evident that rickets is not a disease like 
scurvy, which is a purely vitamin deficiency disease. That 
is, to prevent or cure rickets the mineral compounds con- 
taining phosphorus and calcium must, in the first place, be 
present in liberal quantities in the foods eaten by the child. 
In the second place, foods containing vitamin D must be 
included in the diet or a substance similar in its action to 
vitamin D must be formed in the skin by the action of the 
direct rays of sunlight. 

The lack of sufficient vitamins in the diet causes not only 
specific diseases, but also other alarming symptoms. In- 
sufficient vitamin B causes loss of appetite and digestive 
disturbances. Growth ceases if vitamins A and B are lack- 
ing in the diet. It also seems highly probable that the 
healthy development of the teeth and gums as well as the 
bones is also dependent on the presence of adequate amounts 
of certain vitamins. 

Diet an aid in preventing decay of the teeth. While 
there seems to be a general agreement among dietary and 
dental experts that diet plays an extremely important part 
in the development of the teeth, there is no such unanimity 
of opinion regarding the relation of diet to the prevention 



206 WHAT WE SHOULD EAT AND WHY 

of tooth decay. Some experts in dental science claim that 
it has been demonstrated that decay of the teeth can be 
caused only by acids formed by the fermentation of foods 
due to bacteria clinging to the tooth surfaces, and that 
therefore tooth decay can be prevented only by keeping 
the teeth clean. (See pp. 101 and 102.) Other dental and 
dietary experts assert that they have proof that certain 
factors in the diet are also very important in preventing the 
decay of the teeth. 1 

Light has recently been thrown on this vexing problem 
by Dr. R. Gordon Agnew of West China University. At a 
meeting of the Board of Governors of the university held in 
New York in December, 1932 Dr. Agnew summarized the 
results of his research carried on over a period of four years. 
In the course of his experiments on animals he was able to 
produce evidences of decay of the teeth in nearly one 
hundred per cent of the animals by withholding certain 
food elements. When these food factors were included in 
the diet the incipient decay was arrested. 

The effects of diets containing the food factors referred 
to above were observed in the cases of 450 children in a 
Toronto institution. The observations made during the 
investigation convinced Dr. Agnew that these food elements 
also prevented decay in the teeth of these children. He 
stated that the food elements that brought about these 
remarkable results were phosphorus and vitamin D. He 
found that in the case of the animals the phosphorus 
played the major role, while in the case of the children vita- 
min D was very important. Apparently then the diet 
which has been found effective in preventing rickets should 
also aid in preventing tooth decay. 

1 See " Diet in Relation to the Teeth." in The Newer Knowledge of Nutrition, 4th 
ed., by E. V. McCollum and Nina Simmonds. The Macmillan Company, 1929. 



WHAT WE SHOULD EAT AND WHY 207 

What simple rules should be followed in choosing one's 
diet. It would seem, then, to be comparatively easy for 
parents or even for a boy or girl to choose a hygienic diet, 
for, unless one is sick, one need only heed the following simple 
directions : 

(1) Eat a variety of plant anal animal foods in sufficient 
quantity to satisfy the normal appetite, but do not over- 
eat. 

(2) Include in the diet a liberal amount of the protective 
foods — milk, butter fat, yolk of eggs, fresh vegetables and 
fruits, and the leafy parts of plants in the form of greens and 
salads. 

(3) Drink plenty of water — at least a quart a day. Drink 
at meals if you desire but not while food is being chewed. 

(4) Include in the diet a number of foods that have a good 
deal of cellulose — the coarser vegetables, fruits, whole wheat 
bread, or bran biscuits — to supply " roughage." 

QUESTIONS AND APPLICATIONS 

1. How can you explain the fact that many people are healthy and 
vigorous and yet lack a scientific knowledge of diet ? 

2. Why is a knowledge of food values and diet particularly necessary 
in these days? 

3. Why do people often limit their needed supply of milk, green foods, 
and butter fats ? 

4. How were the uses of each of the classes of food substances deter- 
mined ? 

5. What are the uses of each of the classes of food substances ? 

6. What are the vitamins, and why are they necessary? 

7. State some of the principal sources of each of the classes of food 
substances. 

8. In what way should the amount of each food substance vary for men 
in different occupations ? 

9. How should the amount of carbohydrates compare with the amount 
of protein in the daily diet ? 



208 WHAT WE SHOULD EAT AND WHY 

10. Which classes of foods should be increased in amount if a boy or a 
girl is to engage in hard muscular work or in training for some trying 
athletic activity? 

1 1 . What is the Calorie ? How is the number of Calories a food or fuel 
will yield determined ? 

12. Why is it that .5 of an ounce of butter or of shelled walnuts will 
furnish the same number of Calories that 18.5 ounces of lettuce or 11.2 
ounces of cabbage will furnish? (See p. 196.) 

13. What dietary needs cannot be measured in Calories? 

14. Why is the kind of protein just as important as the amount? How 
is this shown in the experiment with the rats (p. 198) ? 

15. How may protein deficiency be prevented? 

16. Why is one likely to fail to get the right kind of mineral substances 
in proper proportions? 

17. What kinds of minerals are especially needed for building strong 
bones and teeth ? What foods will furnish these in right proportion ? 

18. How may one be fairly sure of preventing a mineral deficiency? 

19. Name and describe four diseases due to lack of vitamins in the diet. 
State the vitamin which is lacking in each case. 

20. What foods will supply the vitamins referred to in 19 ? 

21. Describe the experiments in feeding rats which show the effects 
of the lack in the diet of (a) vitamin A, (b) vitamin C. 

22. State the four simple rules that should guide every boy and girl in 
choosing a diet. 

23. Select from the table (p. 204) all the animal foods and plant foods 
that are excellent sources of vitamin A and arrange them in two columns, 
one for the animal foods and one for the plant foods, and head each of the 
columns, Excellent Sources of Vitamin A. Do the same as above for 
vitamin B and vitamin C. 

24. Which has the better content of vitamin A, the green leaves of the 
cabbage or the leaves in the head of cabbage that have little or no green 
color? (See table, p. 204.) 

25. Compare the vitamin content of egg white and egg yolk ; of butter 
and olive oil and peanut oil. 

26. What is the effect on the vitamin content of rice of removing the 
outer coats, thus forming " polished" rice? 

27. Why did sunshine make such a difference in the two chickens shown 
in the illustration on page 203 ? 






UNIT VII. REPRODUCTION OF LIVING THINGS 
PROBLEM 1. HOW DO ANIMALS REPRODUCE? 

Why new living things are formed. Thus far we have 
considered the methods by which plants and animals, in- 
cluding human beings, live and carry 
on their individual work. It is a fact 
of common knowledge, however, that 
every living thing, after a longer or 
shorter period of life, dies. 1 Certain 
insects, for example, live in the adult 
stage for a few days at most (111. at 
right) ; elephants 'and giant tortoises 
(111. p. 210) may live for several hun- 
dred years ; and some of the towering 
redwood trees (sequoias) of California 
(111. p. 13) began their life from two 
thousand to four thousand years ago. 
But the individual plant or animal, 
even though as long-lived as those we 
have just mentioned, finally dies. 
Hence, the most important part of 
biology, so far as the race is concerned, 
has to do with the methods by which the gift of life is passed 
on from one generation to another. This process is known 
as reproduction. 

How the simplest animals reproduce. The simplest 
forms of plant and animal life are extremely minute and 

1 This is not strictly true in the case of one-celled plants and animals. 

209 




May fly 

This insect lives only one day 

in the adult stage. 



210 REPRODUCTION OF LIVING THINGS 

consist of only one cell. A multitude of these single-celled 
organisms may exist in a drop of stagnant water. If a 
drop of sediment from a stagnant pool is examined with a 
compound microscope, many kinds of microscopic plants 
and animals may be seen. Among them one may discover 
an irregular bit of protoplasm comprising a single cell. 




Courtesy of New York Zoological Society 



Giant tortoise 
This animal from the Galapagos Islands is said to be four hundred years old. 

It may be moving about slowly by a flowing motion of the 
protoplasm. This one-celled animal is called an amoeba 
(d-me'bd). 

The process of reproduction in such a simple animal is 
brought about by cell division y which is carried on in much 
the same way as that already described for the tissue cells 
of the higher plants and animals (p. 24) . This process con- 
sists of a division of the cell nucleus, followed by a division 



ANIMAL REPRODUCTION 



211 



of the cytoplasm (111. below). In the reproduction of the 
amoeba, however, the two cells formed by division do not 
remain attached to each other, as do the tissue cells. In- 
stead they separate into two distinct individuals, each 
having half of the living substance of the parent amoeba. 
Other single-celled animals reproduce in much the same 
way as does the amoeba. 

Why the higher animals must reproduce in a way differ- 
ent from the amoeba. It is, of course, impossible for higher 




C D 

Amoeba in successive stages of division 
Which part divides first ? 

animals (e.g. insects, fishes, cats, and rabbits) to form new 
individuals, as amcebas do, by the process of division into 
distinct individuals. Hence, in order that new animals may 
be formed like those we have just named, certain organs have 
been developed to provide for this function of reproduction, 
just as there are separate organs for digestion and respiration. 
In the reproductive organs there are formed certain cells 
which, after a complicated series of changes, form new 
individuals like the parent. We are now to study the 
method of reproduction as it is carried on by some of the 
many-celled animals. 



212 REPRODUCTION OF LIVING THINGS 

How young fishes are produced from eggs. 1 Anyone who 
has eaten the roe of shad has noticed that this part of the 




Yo/k 



S/'ng/e 
egg ce// 



Devefopfng 

embryo 




A.-Ferti/ized egg 



M-Two ce//ecf stage 
of embrgo 




JDe v e/op/ng 
embrgo 




GrFour ce/ted stage 
of ernbrgo 



D.-Mang ce//ed stage 
of embrgo 




17/nbrgo 




Yo/k.. 

food supp/g ^^^L, ~~~ >_J^y~Yo/k sac 

F.-More fu//g deve/oped K-Young f/sh with c/o/k 

embryo st/// attached 

Modified from Parker and Haswell 

Development of a trout egg 

fish consists of countless tiny spherical objects called eggs. 
Other common animals with which we are familiar — insects, 



1 The roe of fish should be shown in class, and separate eggs should be placed in 
small vials of preserving fluid. These specimens may then be used year after year. 
It is suggested also that, if the studies of reproduction are carried on in the spring, 
the eggs of frogs or toads be secured and placed in aquaria with green water plants 
and that their development into tadpoles be studied. 






ANIMAL REPRODUCTION 213 

frogs, snakes, turtles, and birds — also produce eggs. Under 
natural conditions, after the fish eggs are given off into the 
water, a tiny fish is gradually formed on the outer surface 
of the egg, and the rest of the egg material furnishes the 
necessary food for this process (111. p. 212, A). 

When the fish has reached a certain stage of develop- 
ment, it swims about in the water. Even now, however, 
some of this food material, known as yolk, remains attached 
to the under side of the developing fish (111. p. 212, F). This 
yolk is gradually absorbed by the young fish, and, by the 
time it has disappeared, the young animal is able to secure 
its food supply from the surrounding water. 

Why a fish egg alone cannot develop into a fish. From 
our discussion thus far one might think that a fish egg, if 
placed by itself in the water, would develop as we have 
described. That such is not the case, however, can be 
shown readily if fully developed eggs are gently squeezed 
from the body of a fish into a dish of water. Such eggs, 
instead of forming fishes, soon die. We are now to study 
a most essential step in the production of all many-celled 
animals. 

Were we to visit a fish hatchery some day, at the right 
season of the year, we would see men pressing the sides of 
the bodies of female fish, and thus forcing eggs out into the 
water from an opening situated on the under side of each 
animal (111. p. 214). The workers by gentle pressure also 
secure from male fish a milky material that is very different 
from the eggs. This is known as milt. A fish egg can 
develop into a fish only after one of the microscopic repro- 
ductive cells of the milt has united with it. Neither the 
egg cell nor the male cell in the milt alone can develop into 
a fish. When egg laying takes place naturally, this process 
is known as spawning. 



214 REPRODUCTION OF LIVING THINGS 

What sperm cells are and what they do. What is the 
nature of the material that has been added to the egg cells 
which causes this marvelous transformation from a single 
egg cell into a fully developed fish? If we examine a drop 




Securing eggs and sperm cells (milt) 
The men gently press the sides of the fish. 

of fresh milt under the high power of the compound micro- 
scope, we find innumerable microscopic cells that are swim- 
ming about. These are sperm cells. Each consists of a 
slightly enlarged portion known as the headpiece, which 
contains the sperm nucleus. The rest of the sperm cell con- 
sists of a slender portion called the tailpiece. By the quick 



ANIMAL REPRODUCTION 



215 



Head containing - 
nucleus 



Middle piece 



lashing of this tailpiece a sperm cell swims rapidly through 
the water (111. below). 

A study under the microscope of a drop of water con- 
taining both eggs and milt shows that each egg is surrounded 
by a number of the extremely minute 
sperm cells (111. p. 216, A), each of 
which is trying to force its way into 
the egg by means of its lashing tail- 
piece. A very careful examination 
often shows that the head of one of 
the sperm cells has been forced into 
one of the eggs and that the tailpiece 
has dropped off. The sperm nucleus 
within the headpiece now moves 
toward the nucleus of the egg cell and 
increases somewhat in size. Soon 
the sperm nucleus and the egg nu- 
cleus combine to form a single nu- 
cleus (111. p. 216, C, D). The union 
of sperm nucleus and egg nucleus is 
known as fertilization of the egg. 

How a fertilized fish egg develops 
into a fish. After fertilization has 
taken place, we see the egg nucleus 
dividing into halves (111. p. 212, B). 
These halves move apart, and a cell membrane divides the 
single cell into two cells. Unlike the dividing amoeba, how- 
ever, the two cells remain attached to each other. Each 
of these cells soon divides in a similar way, and so four 
cells are formed (111. p. 212, C). The process of cell division 
continues until there is produced a large number of tiny 
cells, which are apparently all alike, but which really are 
beginning to differ from one another. By these successive 




Head 

containing 
nucleus 



Two kinds of 
sperm cells 

Sperm cells 
Which part of these cells is 
used in locomotion? Which 
part is essential for fertilizing 
eggs? 



216 REPRODUCTION OF LIVING THINGS 

steps a young animal known as a fish embryo is formed, 
which as yet bears little resemblance to the parent fish. 

Presently, however, the head, trunk, tail, and other organs 
of the animal begin to appear (111. p. 212, E, F). When thin 
sections of any of these organs are studied under the micro- 



Egg noe/eus 

Egg nuc/eus 




A -Sperm ce// entering 
an egg ce// 




Nuc/eus of 
sperm ce// 



JB.-Sperm nuc/eus approach/ng 
the egg nuc/eus 





Ferti/ized 
egg nuc/eus 



C- Sperm nuc/eus and D.-Ferti/ized egg nuc/eus 

egg nuc/eus uniting 

Fertilization of an egg 
Note that the egg of this animal, unlike that of the fish, shown on page 212, has no 
yolk, the food being stored in the egg cell. It shows, however, the essential steps in 
fertilization. 



scope, we see rather striking differences in the cells of which 
they are composed. It is evident therefore that, when an 
egg develops, not only does a single fertilized egg cell pro- 
duce many cells (cell division), but also that these cells 
gradually become different in form and function (cell differ- 
entiation), and then growth of these cells takes place. 



ANIMAL REPRODUCTION 



217 



'Spermaries 



Mature eggS"-2 
in ovaries 



The organs concerned in the reproduction of the fish. 
We are now ready to define certain terms that will be used 
frequently in the discussion of the process of reproduction. 
The organs commonly spoken of in the fish as the roe are 
known scientifically as the ovaries (111. below), since in them 
are produced the eggs, or ova (from the Latin, meaning eggs). 
The sperm-producing or- 
gans, on the other hand, 
which are found only in 
the male, are called sper- 
maries. (See 111.) 

Under natural condi- 
tions, when eggs are fully 
developed, they pass out 
of the ovaries into the 
body cavity of the female 
fish. (See 111.). They 
then pass into the egg 
tubes, or oviducts, which 
convey them out of the 
body. In the male fish 
the sperm cells in a simi- 
lar manner are conveyed 
from the spermaries by 
sperm ducts and so are discharged into the water in the 
region of the egg cells. When the nucleus of a sperm cell 
has combined with the nucleus of an egg cell, such & fertilized 
egg cell is ready to develop into a fish embryo in the manner 
already described. 

How the young of fishes are fitted to survive. Most 
fishes, after the eggs are laid and fertilized, have no parental 
instinct and so take no care of their offspring. Indeed, a 
parent fish may even devour its own eggs or young. Since 




~-^Sperm ducts 

^Opening of 
sperm ducts 



Male fish 



Female fish 



Reproductive organs of fishes 



218 REPRODUCTION OF LIVING THINGS 



the eggs of fishes, after being deposited in the water, are 
exposed to so many dangers, relatively few of them will 
hatch, and still fewer of the young will reach maturity. 
Hence, enormous numbers of eggs must be produced. In 
the ovaries of a perch, for example, over 18,000 eggs have 

been counted, and it is esti- 
mated that a large codfish 
(111. p. 467) may deposit 
8,000,000 eggs at spawning 
time. 

To the general rule that 
fishes take no care of their 
young, there is a marked 
exception in the stickle- 
backs, a group of rather 
small fishes found in fresh 
and salt water. The male 
stickleback constructs a 
rather elaborate nest by 
gluing together various 
materials, and in this nest 
several females generally 
deposit their eggs (111. at 
left). The male then de- 
posits sperm cells over the 
eggs, stays about the nest, 
and guards the eggs from 
possible enemies. The male also protects the young stickle- 
backs when hatched. In the numerous American families of 
fresh-water bass and sunfish the parents zealously guard the 
eggs and the young. Among the frogs, toads, snakes, lizards, 
alligators, and turtles, however, the parent animals usually 
exercise no more parental care than do most of the fishes. 




Nest of the stickleback 
Note the eggs within the nest. 



ANIMAL REPRODUCTION 



219 



What advantages the union of sperm cell and egg cell 
affords. Single-celled animals, as we have seen, reproduce 
by cell division. But the many-celled animals which we 
have been studying form new individuals only after the 
union of two different kinds of cells, namely, sperm cells 
and egg cells, neither of which is able to develop inde- 




Courtesy of the late Dr. Jacques Loeb 

Frogs produced from unfertilized eggs 

pendently of each other. This kind of reproduction is called 
sexual reproduction. A second advantage of the union of a 
sperm cell and egg cell from two individuals is the chance 
for variations in the offspring. These variations afford the 
possibility that some of the young may have a combination 
of the superior qualities of the parents and grandparents. 

It is interesting to note that Dr. Jacques Loeb, formerly 
of the Rockefeller Foundation, by a long series of investiga- 
tions, succeeded in causing the eggs of low forms of animal 



220 REPRODUCTION OF LIVING THINGS 

life (sea urchins and marine worms) to develop norms lly 
through the earlier stage by treating the eggs with certain 
chemicals. 1 Dr. Loeb also experimented with frogs' eggs 
by puncturing the membranes with a needle. Eggs treated 
in this way developed through the tadpole stage into adult 
frogs, both male and female. The frogs thus produced looked 
like normal frogs (111. p. 219). 

These experiments show that the chemicals that were used, 
or else the puncturing of the eggs, caused the eggs to develop 
in a manner similar to normal fertilization by sperm cells. 
It seems probable, therefore, that the union of the sperm 
cell with the egg cell is needed to produce chemical or physi- 
cal alterations in the egg, without which the eggs cannot 
develop. 

QUESTIONS AND APPLICATIONS 

1. Give some statements as to the relative length of life of different 
organisms. 

2. What is meant by reproduction? Why is this process necessary? 

3. Describe the various steps in the reproduction of a single-celled 
animal. 

4. Describe the egg and the sperm of a fish. What organs produce 
each of these kinds of reproductive cells ? 

5. How does the sperm cell of a fish reach the egg cell ? What becomes 
of each part of the sperm cell after it reaches the egg cell ? 

6. Give an account of the methods of fish propagation used in the fish 
hatchery. 

7. Describe the development of a young fish from a fertilized egg. 
Where is food material for development secured during this process ? 

8. What takes place during the process of differentiation ? 

9. How are fishes fitted to survive ? 

10. Describe Dr. Loeb's experiments with the eggs of sea urchins, 
marine worms, frogs. What conclusion do you draw as to the effect of 
fertilization ? 

1 The chemical used was a weak solution of acetic acid (like that found in vinegar), 
followed by a treatment with concentrated sea water. 



PLANT REPRODUCTION 



221 



PROBLEM 2. HOW DO PLANTS REPRODUCE? 



Cytoplasm 

Nucleus^ 




How the simplest plants reproduce. Anyone who has 
examined the shady north side of tree trunks has probably 
noticed a thin layer of green material that closely adheres to 
the bark. If a small amount of this green substance is mixed 
with water on a glass slide and examined with a compound 
microscope, tiny green cells that are more or less spherical in 
shape are seen. This single-celled 
plant is known as Pleurococcus 
(ploo'ro-kok'ws). Like the amoeba, 
it reproduces by division of the nu- 
cleus and cytoplasm, and then cell 
walls of cellulose form between the 
" daughter cells" (111. at right). 
In Pleurococcus, however, the new 
cells formed by cell division often 
cling together for a time, and a 
colony of cells is formed thereby. 
Like those of the amceba the daugh- 
ter cells of Pleurococcus, formed by division of the mother 
cell, are, as far as we know, exactly alike. 

How plants are produced from seeds. If we wished to 
get a new supply of bean, pea, corn, radish, or nasturtium 
plants, what steps should we take ? Every one who has cared 
for a garden knows that the soil would have to be loosened 
properly and otherwise prepared, and that seeds would have 
to be put in shallow furrows and covered with earth. From 
these seeds in due time would come plants of the same kind 
as those from which the seeds came. 

In order that new maple or oak trees may be produced, 
it is likewise necessary that seeds of maple trees or of oak 
trees find their way into the earth. These seeds, if supplied 



Three cells 



Four cells 



Reproduction of Pleurococcus 



222 REPRODUCTION OF LIVING THINGS 

with the proper amount of moisture and if favored by tem- 
perature, will sprout. Gradually, a tiny plant (a seedling 
tree) will push its way up through the soil. This later will 
develop into a tree of the kind that produced the seed. 
The first question we might ask is this : Does a young 
plant exist ready formed in the seed, or is the young plant 
formed only after the seed is put into the ground ? 




Placenta^ 



Calyx 
Side view of flower 

First stem 



^-/-Micropyle 
Seed stalk 



Corolla 




Ovules v i 

Wall of ovary 

Section of flower 



Stigma 



Style Mature_ 
seed ~ 
Stamen 




Section of 
mature fruit 



Compound 
leaf 



Seed coats^ 





Cotyledon 



.■'First : ^H&$£- 3P 



Hilum- ^ M i crop yie 

Section of seed 




(3 stages) 



The pea plant 
Which are the nutritive and which the reproductive organs ? 



EXERCISE 51 

Is there a young plant in an unsprouted bean or pea seed ? Lab- 
oratory study or home experiment. 

Materials: Soak some bean or pea seeds for twenty-four hours. 
Remove the seed coats, carefully open the halves, and look within. 

1. Tell what you have done. 

2. If you find any part that looks like a tiny stem, describe it. If 
you find anything that looks like a leaf or a bud (folded leaves), de- 
scribe that. 



PLANT REPRODUCTION 



223 



>Pistil 

'^Stamens 

-—Corolla 
^>Perianth 
~~ Calyx 

Receptacle of 
floral organs 



Axillary bud 



3. What is your conclusion as to the presence or absence of a tiny 
plant in the bean or pea seed? 

Where and when seeds are formed. Bean and pea seeds 
grow in pods (111. p. 222). Other seeds — apple, orange, 
lemon, grape, and pear — are 
found in fruits of the same name. 
Scientifically speaking, however, 
pea and bean pods, tomatoes, 
watermelons, squashes (111. p. 
232), and peppers are just as 
truly fruits as are those we have 
named above, since all of them 
contain seeds. 

A careful dissection of any seed 
will show the presence of an em- 
bryo plant (111. p. 222). The 
question then arises — How are 
fruits with their seeds produced, 
and from what part of a plant do 
they come? If we examine a 
bean or pea plant that has blos- 
somed (111. p. 222), we may find 
not only pods that are mature 
but also those in all stages, some 
even so small that they can 
hardly be seen with a hand lens. 
Indeed, if we dissect a bean or 
pea blossom, we find at the 
very center, a tiny object re- 
sembling a pod in appearance. 
This is the ovary. This organ 
contains tiny ovules which later develop into seeds (111. 
p. 222). 




> — Tap-root 



Courtesy of Brooklyn Botanic Garden 

Parts of a flowering plant 
Name each of the four organs con- 
cerned in reproduction. 



224 REPRODUCTION OF LIVING THINGS 

At the free end of the ovary is usually a slender projection 
known as the style. At the top of the style is a slightly 
enlarged portion called the stigma. The ovary, style, and 
stigma constitute the pistil. The ovary of a flower develops 
into a fruit that contains the seeds. 

In the case of other fruits like those named above (apple 
or grape), we should likewise find their beginning in ovaries. 



Stigma -— 




Fssentiaf 
Organs 



Ovary 



Stem off/o wer 



Parts of a plum blossom 



Hence, it is evident that fruits in general, including the 
seeds that they contain, are somehow formed from the 
ovaries of flowers. We shall now, therefore, direct our study 
to the structure and functions of flowers. 

The organs of flowers. When we come to examine almost 
any common blossom (111. pp. 223, 224), we easily find at its 
base an outer circle of rather small leaflike parts. This 
circle as a whole is known as the calyx (ka/liks, Latin, mean- 
ing cup). Each of its subdivisions is called a lobe of the 



PLANT REPRODUCTION 



225 



calyx ; or if its parts are separate, each is called a sepal (se'pal). 
Inside of the calyx is a second circle of parts usually brightly 
colored ; this is the corolla (ko-rol'd, Latin, meaning small 
crown), each of its parts being known as a petal. Within 
the corolla is a third 
circle of rather slender 
parts. Each is called a 
stamen and consists of a 
threadlike stalk, the fila- 
ment (from the Latin, 
meaning thread), and an 
enlarged top, the anther. 
In the anthers is pro- 
duced a powdery sub- 
stance known as pollen. 
In case the two outer 
circles of a flower are 
much alike in form and 
color, as in the tulip, 
gladiolus, or lily (See 
111.), all these leaflike 
parts taken together are 
called the perianth (per'i-anth, Latin, meaning around the 
flower). In any flower, however, the calyx and corolla to- 
gether may be called the perianth. 

EXERCISE 52 
What are the parts of the tulip flower ? * Laboratory study. 

1. On the outside of the flower are brightly colored leaflike parts 
arranged in two circles, making up the perianth. 

a. Of how many leaflike parts does the perianth consist? 



4. V 






%pC 


r ■'".'•'- 


^V f\ 




i flik 



Courtesy of Brooklyn Botanic Garden 

Wood lily 
The six parts of the perianth are similar. 



1 These directions with some modifications will apply to flowers like the lily or 
gladiolus. 



226 REPRODUCTION OF LIVING THINGS 

b. State the color of their parts. 

c. Draw (natural size) one of the divisions of the perianth. Label : 

Segment of perianth. 

2. Inside of the perianth note the circle of stamens. 
a. State the number and the location of the stamens. 

6. Draw (natural size) one of the stamens. Label : Anther, Fila- 
ment. Underneath write : One of the stamens. 

3. At the center of the blossom note the triangular ovary and, 
above it, the three lobes of the stigma. The ovary and the stigma 
are the parts of the pistil, there being no style in this flower. 

a. In what region of the flower is the pistil found? 

b. Make a drawing (natural size) of the side view of the pistil. 

Label: Lobes of stigma, Ovary; and beneath your drawing 
write : Parts of the tulip pistil. 

4. We have found that the tulip flower consists of three different 
kinds of organs. Name in order of position, from the outside to the 
pistil in the center, the three kinds of organs, and give the parts of 
each. 

EXERCISE 53 

What are the essential organs of a flower, and what is the use of 
each? Laboratory study. 

Materials: Flowers of tulip, Easter lily, gladiolus. 

1. Cut a thin cross section of the ovary, place it on a black back- 
ground, and study it with a hand lens. The tiny white objects are 
ovules (111. p. 222), which develop into seeds. 

a. Where are the ovules found? 

6. Are the ovules attached to the outer wall of the ovary or to the 

central region ? The region of attachment of an ovule or a seed 

is known as a placenta (pld-sen'td). 

c. What is the placenta? 

d. Make a drawing (X 4) of the cross section of the ovary and of its 

contents. Label : Wall of the ovary, Ovules, Placenta. Beneath 
the drawing write : Cross section of the ovary of a tulip X 4- 

2. Study the ripened anthers in a blossom and find a powder 
(pollen) escaping from them. 

a. Where are the pollen grains produced? 

b. What is the color of the pollen you are studying? 



PLANT REPRODUCTION 227 

3. Rub the finger tip or a camel's-hair brush on a ripe anther from 
which pollen is being discharged. Now gently touch the surface of the 
stigma of the same flower or of another flower of the same kind. 

a. This process we have just performed is a form of "pollination. 

Describe the experiment in pollination. 

b. State whether or not the pollen is held by the stigma ; and if so, 

how. (Use a hand lens for this purpose.) 



EXERCISE 54 

What are the parts of the flower of the butter-and-eggs plant or of 
the garden snapdragon? Laboratory study. 

Materials: Plants that have flowers and well-developed fruits. 

1. Cut a thin cross section of a well-developed ovary (fruit). Place 
the section on a black surface and examine it with a hand lens. 

a. Are the seeds many or few ? 

b. Are the seeds attached to the outer wall of the ovary or to the 

central region? The region of the ovary to which the seeds 
are attached is known as a placenta. 

c. What is the placenta ? 

d. By the aid of a hand lens make a sketch (X 4) of the cross section 

of the ovary and its contents. Label : Wall of the ovary, Seeds, 
Placenta. Beneath the drawing write : Cross section of the 
ovary of butter-and-eggs (or of snapdragon) (X 4). 

2. Secure a fully opened blossom, grasp the colored parts near the 
top, and carefully pull them off, keeping these parts for further 
study. 

a. In what region of the flower is the pistil found? 

b. Note the ovary and a slender, white projection, the style, above 

it, at the top of which is an enlarged region, the stigma. The 
ovary, style, and stigma are parts of the pistil. Make a 
drawing (X 4) of the side view of a pistil and label: Ovary, 
Style, Stigma. Beneath the drawing write : Pistil of butter-and- 
eggs (or of snapdragon) ( X 4) . 

c. Cut a thin cross section of the ovary, place it on a black surface, 

and study it with a magnifying glass. The tiny white objects 
are ovules, which develop into seeds. Where are ovules found? 
How do ovules differ in size from seeds? 






228 REPRODUCTION OF LIVING THINGS 

3. Open the two lips of the yellow and orange portion of the flower 
that you removed when studying the pistil. This is called the corolla. 

a. Notice slender objects attached to the inner surface of the corolla. 

These are the stamens. How many stamens do you find, and 
how do they differ? 

b. Each stamen consists of a slender stalk known as the filament and 

an enlarged top called the anther. Draw one of the stamens 
(X 4) and label : Filament, Anther. Beneath the drawing write : 
One of the sta?nens ( X 4) . 

c. Study the anthers in a blossom and find a powder escaping from 

each. This is pollen. By means of the finger transfer some of 
the pollen to a glass slide and examine it under the low power of 
a compound microscope. Where are pollen grains produced? 
Draw several of the pollen grains as they appear to you and 
label : Pollen grains highly magnified. 

4. At the base of the ovary notice small leaflike objects. They are 
the sepals. How many sepals do you find? Add the sepals to your 
drawing in 2 above and label them. The circle of sepals is known as 
the calyx. 

5. We have found that the flower of butter-and-eggs consists of four 
different kinds of organs. Name in order of position, from the outside 
to the pistil in the center, the four kinds of organs and give so far as 
you can the parts of each. Make a drawing (natural size) of the side 
view of the open blossom and label parts. 

Note. If flowers are studied in the autumn, the experiment in 
pollination should be performed at this time, using gladiolus or canna 
blossoms for this purpose. (See Exercise 53, 3.) 

How a plant embryo is formed by the union of a sperm 
cell with an egg cell. In the many-celled fish which we 
studied in the preceding problem we found that the embryo 
was formed from a fertilized egg cell. Is this likewise true 
in a flowering plant ? Our first problem is that of determin- 
ing whether or not egg cells and sperm cells are present in 
such a plant. Microscopic study of the plant ovule shows 
that it consists of two outer coverings, or coats, made of 
cells and that within the fully developed ovule are other cells, 






PLANT REPRODUCTION 



229 



?o//en grains 

v //en grain 
/Stigma 



Stg/e 



Po/ien tube 



■Egg ceff 



one of which is an egg cell (111. below). Hence we see that 
the ovule rather than the ovary corresponds in function to 
the ovary of a fish. In a similar way it has been proved 
that pollen grains (111. p. 230) have cells that correspond 
in function to the 
sperm cells of the 
fish. 

In studying the 
fish, we found that, 
before development 
could take place, a 
sperm nucleus and 
an egg nucleus must 
unite. This union 
must also take place 
in a flowering plant. 
Let us now consider 
how it is possible 
for the sperm nu- 
cleus of a pollen 
grain to reach the 
egg nucleus of an 

Ovule in the Ovary. Fertilization of an egg cell in an ovule 

In the Case Of the Tra ce the course of the fertilizing nucleus of a pollen 

n 1 ,i ii grain from the anther to the ovule. 

fish, the sperm cell 

could swim to the egg cell. Since, however, stamens and 
pistils are surrounded by air and not by liquids, and since 
pollen has no means of locomotion, some other method of 
transfer must be possible. 

How pollen is carried to the pistil. In some flowers the 
filaments support the anthers in such a way that the pollen 
can be discharged readily upon the surface of the stigma 
of the same flower when the stigmatic surface is ready to 




Ovary waif 



Peta/ 



Sepaf 



230 REPRODUCTION OF LIVING THINGS 

receive it. In cases like this, pollination is, of course, a simple 
process. Again, when pollen is light and powdery, it is 
readily blown about by the wind, as is the case especially 
in the inconspicuous flowers of the grasses and corn 
(111. p. 231). In these plants the stigmas are distinctly 
feathery or hairy in order to catch the flying pollen. 

Many flowers, however, have pollen so situated that it 
cannot fall upon the stigma ; indeed, plants like the squash 



Sperm ^ ; 
nuclei 




Cross section of a Germinating pollen 
pollen grain grains 



Different kinds of pollen 
{highly magnified) 
Redrawn from Transeau's "General Botany' 



Different types of pollen 



have two kinds of flowers : one having stamens and no 
pistil (111. p. 232) ; the other a pistil and no stamens (111. 
p. 232). In other kinds of plants the pollen may ripen at 
a time when the stigma is not ready to receive it. Again, 
the pollen may be too sticky to be easily detached and 
carried by the wind ; in those cases there must be some 
agency of transfer other than gravity or the wind. 

When the blossoms of fruit trees or of clover plants open, 
they frequently are visited by bees. If we watch the bees, 
we shall see them thrusting their sucking tongues deep into 
the fragrant blossoms in search of their food. As the bees 
push their way into the flowers, their hairy tongues, heads, 
and legs become coated with the sticky pollen that is 
discharged from the anthers of the stamens. When the 



—yStaminate fbwers 




Single flower 
of tassel 



Com plant 





Endo- // Ovary 

sperm j / * W— Embryo 



Section of 
com grain 



Ear of com 

The corn plant 
Which are the nutritive and which the reproductive organs ? 



232 REPRODUCTION OF LIVING THINGS 

insects fly to other blossoms, pollen is carried along and some 
of it will be left on the stigma of the projecting pistil. But- 
terflies, moths, and some other kinds of insects also carry 
pollen, but honeybees and bumblebees are far more impor- 
tant in pollination. 

Most flowers that are pollinated by insects are dis- 
tinguished by colors and odors that are believed to at- 




Staminate blossom 



Pistillate blossom 



Squash blossoms 



tract the insects. In these cases the insects are repaid for 
their visits by securing a sweet liquid, known as nectar, 
which is secreted in nectar glands. Bees use this nectar 
in making honey. Flowers, the pollen of which is car- 
ried by the wind, such as those of corn and grasses, have 
small inconspicuous flowers that lack bright colors and sweet 
odors. 

Pollination may be defined as the transfer of pollen from the 
anther of a stamen to the stigma of a pistil. If the transfer 
is made from the stamen to the pistil in the same flower or, 
more precisely, to the pistil of another flower on the same 
plant, the process is known as self-pollination. In cross- 



PLANT REPRODUCTION 233 

pollination the pollen is carried from the anther of one flower 
to the stigma of another flower of the same kind but on a 
different plant. 

EXERCISE 55 

What changes take place in the pollen when it reaches the stigma ? 

Laboratory demonstration. 

Material: Ripe stigmas of flowers such as Easter lily, tulip, canna, 
gladiolus, or tiger lily, that have been pollinated at least six to twelve 
hours previously. 

1. Cut off a very thin slice horizontally from the surface of the 
stigma, place it on a glass slide with several drops of water, and mash 
the section thoroughly with a knife blade. Cover with a cover glass 
and examine with the low power of the compound microscope. Find 
a pollen grain that has begun to form a projection, that is, a pollen 
tube. 

2. Make a drawing of various stages of the germinating pollen and 
an unsprouted pollen grain. Label : Pollen grain, Pollen tube, Un- 
sprouted pollen. 

How a sperm nucleus reaches and fertilizes an egg cell. 

After pollination is accomplished, pollen grains are held to 
the stigma by hairs or by a sticky secretion or by both. 
From the stigma the pollen grains absorb food substances 
and a pollen tube begins to grow from each grain (111. 
p. 229). Each pollen tube makes its way downward be- 
tween the cells of the stigma and style until it reaches the 
small opening in an ovule. This opening is the micropyle 
(ml'kro-pll, Greek, meaning small gate). After entering the 
micropyle, the tip of the tube opens and the protoplasmic 
material within the tube, which includes two sperm nuclei, 
is forced into the ovule (111. p. 234). One of the sperm 
nuclei finally reaches and unites with the nucleus of the egg 
cell. Thus fertilization of the egg cell is accomplished (111. 
p. 234). 



234 REPRODUCTION OF LIVING THINGS 



How a fertilized egg cell develops into a plant embryo. 

The egg cell after fertilization divides in half in a way similar 
„ .. „ . to cell division in 

4 Coatings ofovu/e 
Sf 

fFgg-ceii n uc/eus 

f ^Sperm nuc/e/ 




— Fo//en tube 



before fertilization of egg ce// 




jFgg nuc/eus and sperm 
// nucleus uniting to form 
fert/7/zed egg ce// 



Ferti/ization of egg ce// 

Fmbrgo-sac wa// 

y Se e d /ea ves 

Deve/oping embngo 

—Stem region 

Foot region 
~ =r - i ~ Suspensor ce//s 

•Coatings of ovcz/e 
Far/y stage of embri/o 

Formation of a plant embryo 




the egg of a fish, and 
division continues 
until many cells are 
formed. The cells 
become different in 
structure and func- 
tion (cell differenti- 
ation) and gradually 
form the parts of 
the tiny plant, or 
embryo, which we 
found in the seed 
(See 111. p. 222). 
Materials for further 
growth are supplied 
by the mother plant 
through the sap 
tubes that run from 
the stem to the de- 
veloping embryo. 
In all these studies 
we notice that re- 
production does not 
take place until the 
plant or animal has 
reached its matu- 



rity, since the reproductive process makes a considerable draft 
on the nutritive resources of the plant or animal. 

And so we see that, before an egg cell of an ovule can 
develop into an embryo, pollen must be transferred from 



PLANT REPRODUCTION 235 

an anther to the stigma (pollination), the pollen grain 
must form a pollen tube (germination of the pollen grain), 
and the sperm nucleus and egg nucleus must unite (fertili- 
zation) . 

How the young of the higher seed plants are fitted to sur- 
vive. 1 The embryos of flowering plants are not only sup- 
plied directly with food materials during the early stages of 
development but are also given a store of sufficient food in 
the seed, either in the embryo itself, as in the bean or pea 
(111. p. 222), or around it, as in the corn grain (111. p. 231). 
To a certain extent, also, the growing embryo is protected 
within the mother plant and is provided with seed coats 
that later may become relatively thick and hard. 

If the seeds of plants were to start their germination close 
to the parent plant, most of them would perish from lack of 
water and mineral matter and sunlight. Hence it is advan- 
tageous for seeds to be scattered rather widely so that the 
young plants may secure favorable conditions for growth. 
Many kinds of seeds, or fruits, seem specially fitted for dis- 
persal by the wind. Examples of winged fruits (i.e. fruits 
provided with broad and thin surfaces that are blown by 
the wind) are those of the maple, elm (111. p. 236), and lin- 
den. Some with tufts of hair attached to the upper end 
of a stalk are the tiny fruits of the dandelion and thistle and 
the tufted seeds of the milkweed. 

Other common fruits like the cocklebur, burdock, and 
other " sticktights " (111. p. 237) have sharp hooks, or barbs, 
which catch in the hair of animals and so either the seeds 
or fruits are often carried for some distance from the 
parent plant before they become detached. 

1 Before assigning this section for study, the teacher should, as far as possible, 
demonstrate the various methods of seed protection and dispersal and stimulate 
pupils to do as much field work as they can profitably undertake. 



236 REPRODUCTION OF LIVING THINGS 

Still another method of seed dispersal is that seen in fleshy 
fruits like the brilliant cherry and berries of various kinds. 

Birds are attracted 
by the bright colors 



nl 




. i !^W of these fruits when 

they become ripe. 

In the case of fruits 

"stem like cherries, the 

Dandelion Clematis Elm Maple birds eat the fleshy 

fruit fruit fruit fruit 

pulp and drop the 
Fruits and seeds dispersed by wind , -, . , / -, 

hard pits (cherry 

seeds). In the case of raspberries and blackberries the 
seeds are so small that they are eaten with the pulp, and 
being hard and indigestible they are dispersed with the other 
body wastes. Squirrels, too, in their attempts to hoard 
nuts for a winter supply, often bury them in the ground or 
drop them before reaching the hollow trees selected for stor- 
age. Some tiny seeds stick to the feet of birds and other 
animals. Still other fruits or seeds like the coconuts are 
carried for some distance on the surface of water. 

Advantages of cross-pollination. In some plants cross- 
pollination, instead of self-pollination, is essential, otherwise 
no fruits are formed. Even when fruits will develop as a 
result of self-pollination, repeated experiments have shown 
that far better crops can be obtained if the pollen is carried 
to the pistil of another plant of the same kind. On page 237 
is a striking proof of the necessity of cross-pollination in- 
stead of self-pollination in blueberries. This experiment 
was one of many carried on by Dr. Frederick V. Coville, 
Botanist of the United States Department of Agriculture, 
Washington, in connection with his work on the cultivation 
of blueberries. In the picture are shown two twigs of a 
blueberry bush, both of which had the same number of 



PLANT REPRODUCTION 



237 





Cocklebur Tick trefoil Burdock Beggar ticks 

Fruits and seeds dispersed by animals 



flowers. Both grew on the same bush and in equally good 
situations. Both twigs were photographed on the same 
day. 

Before the flowers 
were ready for polli- 
nation the stamens 
were removed from 
each in order to pre- 
vent possible self- 
pollination. The 
pistils of the flowers 
on the left-hand side of the picture were then carefully sup- 
plied with pollen from flowers on the same bush (in other 
words, self-pollination was carried on). Each of the flowers 
on the twig at the right side of the picture was treated with 
pollen taken from flowers on another bush (cross-pollination) . 

This experiment was 
performed in a green- 
house where insects 
could not have access 
to the flowers. After 
pollination the fruits 
were allowed to de- 
velop. 

The result, as you 
can see, is most strik- 
ing. The self-polli- 
nated pistils pro- 
duced no ripe fruit. 
All the fruit that 
formed on the branch 
at the left remained small and green, and all but two dropped 
off before the photograph was taken. The cross-pollinated 




Self- 



Courtesy of Dr. Frederick V. Coville 

and cross-pollination in blueberries 



238 REPRODUCTION OF LIVING THINGS 

flowers, on the other hand, produced a full cluster of ripe, 
handsome fruit. Hence, in order to get any kind of satis- 
factory blueberry crop, it is necessary that cross-pollination 
be carried on by the bees, or other agency. It is evident, 
also, that if one is to develop a successful blueberry planta- 
tion, the blueberry plants must not all be propagated from 
one parent bush. 

QUESTIONS AND APPLICATIONS 

1 . How do the simplest plants reproduce ? 

2. What are some of the steps necessary to produce vegetables or 
flowering plants in our gardens ? 

3. Describe the part of a young plant (embryo) that you found in some 



4. Name the part of a plant in which seeds are formed. 

5. Describe the various kinds of organs that are found in some flower 
with which you are familiar. Which of these organs are essential for the 
production of an embryo, and what is the use of each ? 

6. What is meant by pollination? Describe several adaptations for 
this process. 

7. Give an account of the germination of pollen grains. 

8. What is the function of the pollen tube ? 

9. Is the ovary of a flower or the ovule in the ovary more like the ovary 
of a fish in function ? Explain. 

10. How does the pollen tube get into the ovule? What must now 
occur before fertilization can take place ? 

11. Describe the development of a fertilized egg cell into a plant 
embryo. 

12. How is the plant embryo supplied with food during the early stages 
of germination ? 

13. Why is it necessary that seeds be carried away from the mother 
plant? 

14. Describe several methods by which seed dispersal is accom- 
plished. 



PLANT PROPAGATION 239 

PROBLEM 3. HOW IS PLANT PROPAGATION CARRIED ON? 

Seeds and Their Development into Plants 
EXERCISE 56 

Study of the bean seed and the development of the bean seedling. 

Laboratory study. 

Materials: Dry bean seeds and seeds that have been soaked for 
twenty-four hours ; sprouted bean seeds and seedlings grown as fol- 
lows : To secure early stages, cover seeds that have been soaked fo>' 
twenty-four hours with moist sawdust or Sphagnum, and allow them to 
stand in a warm place for two or three days ; for older stages of bean 
seedlings, plant soaked seeds in boxes containing a mixture of moist saw- 
dust and earth. If some of these boxes are put in a warm place and 
others in a cool place, all stages may be obtained in two to four weeks. 

1. What difference do you note in the size of the dry and soaked 
seed ? How do you account for this difference ? 

2. On one edge of a soaked seed find a scar (the hilum, hi'l#m), which 
marks the place where the bean was attached to a small stem that con- 
nected it to the pod. Locate the hilum and state how it was caused. 

3. Pinch a soaked seed and note an opening near the hilum through 
which water is forced from the seed. This is the micropyle, the opening 
through which the pollen tube entered the ovule. 

a. Describe the position and appearance of the micropyle. 

b. What is one use of the micropyle during the development of the 

seed (p. 234)? 

c. What do you notice at the end of the hilum opposite the mi- 

cropyle ? 

4. Make a sketch of the bean seed (X 2), showing the surface where 
the scar is found, the outline of this edge of the bean, the elevation, the 
hilum, and the micropyle. Label each of these parts and the drawing 
as a whole. Draw also a side view of the bean seed, showing as many 
parts as possible, and label them. 

5. Carefully remove the seed coat and then one of the halves. Each 
of the halves of a bean seed is known as a cotyledon (kot'i-le'dwn) or 
seed leaf. Place the cotyledon at one side but close to its point of 
attachment to the small stem (also known as hypocotyl, hi-po-kot'il). 
Make a drawing (X 2) showing the parts of the bean embryo. Label 



240 REPRODUCTION OF LIVING THINGS 

the two seed leaves, or cotyledons, the first stem, or hypocotyl, and 
the first bud, or plumule (ploo'mul). Label the drawing as a whole. 

6. Examine a bean seed that has just begun to sprout. 

a. Name the part of the bean embryo that first breaks through the 

seed coats. 

b. Make a drawing (X 4) showing the side view of the sprouted 

seed. Label the whole, and the part named in a. 

7. Look at a pot of young seedlings that are just pushing their way 
above the surface of the soil or sawdust. 

a. What part of the embryo first appears above ground? 
6. What is the shape of this part? 

8. Study a whole bean seedling that has just emerged from the soil. 

a. Describe the changes that take place in each part of the embryo 

after the seed begins to sprout. 

b. Describe the position and the appearance of the main root and of 

its branches at this stage. 

c. Make a drawing (natural size) of a seedling at this stage and show 

by a horizontal line the ground level. Label each part. 

9. Study a well-developed bean seedling, comparing it with the 
stages already drawn, and answer the following questions : 

a. What changes in the size of the cotyledons do you note as the 

seedling grows older? Most of the food for the early develop- 
ment of the seedling is furnished by the cotyledons ; suggest, 
therefore, the cause of the change in size of the cotyledons 
which you have noted. 

b. What parts of the developing embryo change in color during ger- 

mination? How do they change? 

c. What parts of the seedling have developed from the plumule ? 
10. Draw a well-developed bean seedling and label the Main root, 

Root branches, Ground level, Cotyledons, Hypocotyl, Epicotyl (ep'i-kot'il, 
stem above cotyledons), Leaves of plumule, and Terminal bud. 

EXERCISE 57 

Study of the corn seedling and its development from the corn grain. 

Laboratory study. 

Materials : Dry and soaked corn grains ; seedlings of various sizes 
grown as described above for the bean seedling. For our purpose corn 
grains should be planted with the pointed end down. 



PLANT PROPAGATION 241 

The structure of the corn grain and the development of the corn em- 
bryo can be understood much more easily if the study of the corn seed- 
ling is made first and later that of the corn grain. 

A. Seedling just breaking ground. 

1. Examine a pot of seedlings that are just pushing their way 
through the soil or sawdust and study a seedling at this stage. All the 
parts of the seedling above the corn grain have developed from the first 
bud, or plumule. 

a. What is the shape of the part that first breaks through the soil ? 

b. Look for the sheath leaf surrounding the unfolding leaves and trace 

it down to the ridge around the stem from which it springs. 
How does this sheath, or first leaf of the plumule, differ from 
the unfolding leaves ? What is its probable use ? 

2. Observe the scar on the grain that shows where it was fastened to 
the cob and note the shape of the grain at its opposite end. Does the 
plumule develop from the blunt end or the pointed end ? 

3. Make a sketch of the seedling (X 2) and label: Grain of corn, 
Scar where grain was attached to the cob, Stem of plumule, Sheath leaf, 
Unfolding leaf, Main root, Rootlets, Soil line. 

B. Corn grain just sprouting. 

1. Examine a corn grain that has just sprouted. Recall to mind the 
end of the grain from which the main root grew. (If you are not sure, 
look at your drawing or, better yet, at the seedling.) 

a. What part of the little corn plant breaks through the covering first ? 

b. What other part of the embryo shows signs of growth? 

2. Remove the thin covering from the grain and observe an oval body 
embedded in the corn grain. This is the little corn plant, or embryo. 
How does the embryo differ in color from the rest of the grain ? 

3. The oval-shaped body from which the root and plumule seem to 
spring in the grain of corn is the cotyledon. The remainder of the grain 
is food material (endosperm) for the development of the embryo. 
Make a sketch (X 2) of the seedling at this stage and label : Single 
cotyledon, Plumule, Endosperm, Main root. 

C. Corn grain. 

1. Very carefully scrape away a little of the surface of the cotyledon 
of a dry or soaked grain till the other parts of the plant embryo come 
into view. Identify the plumule and main root. 



242 REPRODUCTION OF LIVING THINGS 

Sketch the corn grain and label : Cotyledon, Plumule, Tiny root, 
Endosperm. 

2. Cut a corn grain in such a way as to divide the embryo and endo- 
sperm lengthwise in half. Put one half in an iodine solution. Where 
in the corn grain is starch present ? Where is it absent ? 

D. Corn seedling well advanced. 

1. What changes in the roots have taken place during the develop- 
ment of the seedling ? What changes in the plumule ? 

2. How does the veining of the leaves in the corn plant differ from 
that in the leaves of the bean plant ? 

3. Where do you find aerial, or air, roots on the corn seedling? 
(Roots growing above ground are aerial roots.) 

4. Pinch the grain between your fingers. What changes do you 
note in the amount of food material ? How can you account for these 
changes ? 

5. Make a sketch of the seedling and label : Corn grain, Cotyledon, 
Stem, Leaves, Aerial roots, Soil roots. 

What a seed is. The most important part, evidently, 
of a bean seed and of a corn grain is the tiny embryo. This 
is true of all seeds. But the embryo is only a part of the 
bean seed since the embryo is protected by a covering, which 
is composed of coatings (seed coats) derived from the ovule 
(111. p. 234). Also the cotyledons of the bean embryo are 
much enlarged to hold the food for the early growth of the 
tiny plant. Likewise the corn grain is provided with a store 
of food inside the single cotyledon of the embryo and a much 
larger store of food outside the embryo in the endosperm 
(111. p. 231). We may therefore say that a seed is an embryo 
plant provided with food and protected by coatings. 

How seeds differ. First, seeds vary greatly in size. As 
an illustration of the wide range of difference in this respect, 
we may compare the tiny bird seed and the coconut. Sec- 
ond, seeds differ with reference to each of the three parts 
named above : embryo, food supply, and coatings. 



PLANT PROPAGATION 



243 



The bean or pea embryo has two cotyledons (111. p. 222), 
and the corn has one (111. p. 231). Some embryos, however, 
have more than two cotyledons ; the pine tree is an example 
(111. below). Seed plants have been classified according to 
the number of the cotyledons found in the embryo. Hence 



Pine leaves ^-...^ 
(needles) 



Cotyledons ** 





The pine seedling 
How many cotyledons has the pine seed ? 

we have all plants in which the embryos develop two coty- 
ledons grouped together. These plants are called dicotyle- 
dons (di-kot'i-le'dimz, Greek, di — two + cotyledons) (111. 
p. 321). Beans, peas, squashes, and castor beans are exam- 
ples of dicotyledons. The plants like the corn, in which the 
embryos have only one cotyledon, are called monocotyledons 
(mon'o-kot'i-le'dtfnz, Greek, mono = one + cotyledons) 
(111. p. 320). Examples of monocotyledons are the grasses, 



244 REPRODUCTION OF LIVING THINGS 



to which the corn belongs, all members of the lily family, 
and palm trees. The pines, hemlocks, spruces, and firs may 
be called poly cotyledons (p6ri-k6t / i-le'd#nz). The embryos 
of seeds differ in structure in other respects, but the number 
of cotyledons furnishes the most striking variation. 

The location of food stored furnishes another point of dif- 
ference. Thus bean, pea, and squash seeds have the food 

stored in the cotyledons ; that 
^- Hypocotyl 



One of the two 
i cotyledons 



Z^Seed coats 




is, in the embryo. This is also 
true of a large number of 
kinds of seeds. In the corn, 
however, the greater amount 
of food is found outside the 
embryo. In the castor bean 
and pine seeds practically all 
the food is stored outside the 
embryo, the cotyledons being 
very thin in the castor bean 
and slender in the pine seed. 

The relative amounts of the 
food substances also vary some- 
what. Thus beans and peas 
are rich in both proteins and 
starch, but contain extremely small percentages of fat. Cas- 
tor beans are rich in oils and proteins and contain practically 
no carbohydrates. Corn grains have a rich supply of starch 
in the endosperm, a good proportion of fat in the cotyledons, 
and proteins in both. Pine seeds, like corn grains, are well 
supplied with carbohydrates, proteins, and fats. 

How the embryos of seeds differ in their development. In 
all kinds of seeds the root system develops somewhat ahead 
of the other parts of the embryo, and thus the little plant 
secures a very necessary hold on the soil. In the develop- 



~ N Secondary roots 
root 



Germination of the castor bean 

Which part of the seedling first appears 

above the ground ? 



PLANT PROPAGATION 



245 



ment of the other parts of the embryo there is considerable 
variation. In the bean, castor bean (111. p. 244), pine, and 
squash embryos the hypocotyls elongate quite rapidly and 
carry with them, therefore, the cotyledons which inclose the 
developing plumule. Since the hypocotyls of the embryos 
of the bean, castor bean, squash, and pine seeds emerge from 
the soil in the form of arches, the cotyledons and any other 
parts inclosed in the seed coats are 
pulled out of the soil instead of being 
pushed out (111. p. 246). The hypo- 
cotyls of the pea (111. p. 222), Windsor 
bean, and corn grow in length scarcely 
at all. Consequently the cotyledons re- 
main underground, and the stem of the 
plumule in the pea and Windsor bean 
pushes through the soil in the form of 
an arch. In corn, oats, and wheat em- 
bryos (111. at right), the plumule is pro- 
tected by a sheath leaf, and the whole 
tapers to a sharp point. Such plu- 
mules come out of the ground straight 
and not in the form of an arch. 

The cotyledons of embryos like those of corn, pea, and 
Windsor bean cannot, of course, serve as foliage leaves at 
all since they remain underground. The cotyledons of the 
bean come above ground and, though they turn green and 
seem to function as green leaves, they do not long remain 
and so are not serviceable to any extent as foliage leaves. 
The cotyledons of seeds like the squash (111. p. 246) and 
castor bean come above ground, turn green, and serve as 
the first foliage leaves of these seedlings. In the bean, pea 
(111. p. 222), and corn embryos the leaves of the plumule are 
the first foliage leaves. 




Wheat seedling 



246 REPRODUCTION OF LIVING THINGS 



Plant grafting. The method of perpetuating a desirable 
plant variety by means of seeds cannot, of course, be used 
in the case, for example, of seedless oranges. All the trees 
that bear this kind of fruit have been produced from a single 
tree which was discovered to have this characteristic. The 
method adopted here is known as grafting, which we shall 
now consider briefly. A young shoot, known as a scion 
(111. p. 247), is cut in an oblique direction from an orange 



Foliage leaves 




Stages in the development of the squash seedling 

tree that bears the seedless fruit, and a similar oblique cut is 
made across the twig of an ordinary orange tree, called the 
stock. The two freshly cut surfaces are then closely applied 
to each other, and the scion and the stock are bound together 
by grafting wax, which is put around the outer bark to hold 
the two pieces in place and to prevent evaporation of water. 
In this way the growing layers (cambium) of the two plants 
are brought into close contact and soon unite. The ducts 
and sieve tubes of the stock likewise join those of the scion, 
and so sap is transmitted to and from the grafted twig, which 
grows and develops its seedless fruit as though it were still 
a part of the plant from which it was taken. 



PLANT PROPAGATION 



247 



There are many different ways of cutting and bind- 
ing the twigs together, and even buds may be used as 
scions. But the principle is the same in every case. Graft- 
ing is also frequently used to combine the desirable char- 



|V_ 7 Scions^^^ 



Scion 




Stock 



Bud - grafting 
Methods of grafting 

acteristics of two different plants (111. above). For ex- 
ample, when the vineyards of France were being destroyed 
by an insect that attacked the roots, the fruit-growers 
overcame the difficulty by grafting the scions of wine-pro- 
ducing grapes upon the more vigorous and resistant stock 



248 REPRODUCTION OF LIVING THINGS 



of grapevines introduced from America that are immune 
from the disease. 

Methods necessary for increasing crop production. The 
farmers of the future, to be successful, must be able to select 

the best seeds, and to 
take advantage of breed- 
ing experiments made by 
others. They should know 
the principles involved 
in thorough cultivation of 
their crops and in the ap- 
plication of manures and 
fertilizers. They should 
determine by experiments 
the types of crops best 
adapted to the soil on their 
farms, and should by 
proper rotation of their 
crops (that is, by sowing 
clover or other nitrogen- 
fixing plants one year and 
corn or other crop the 
next) increase rather than 
decrease the fertility of 
their soil. If the farmer 
is a fruit grower, he should 
know how to prune his 
trees properly, and he 
should practice grafting in 
order to secure better types of fruits. If he has soil adapted 
for woodland, he may plant forest trees, and put into effect 
the principles of forestry (111. p. 313). In fact, there are 
countless ways in which the farmer of the future may in- 




Courtesy of Brooklyn Botanic Garden 

Grafting 

A tomato grafted on a potato. Note the 
tomato on the stem and the potato on the soil 
surface. 



PLANT PROPAGATION 249 

crease the yield from his acres if he but uses his intelligence 
as well as the labor of his hands. It is most important for 
all of us that he do this, for in the last analysis every one of us 
is dependent on him for a sufficient supply of nutritious food. 

Conditions Essential for the Growth of Plants 

Five conditions essential for the growth of green plants. 

Light, air, moisture, and favorable temperature are essential 
to plant growth. We have shown in Exercise 18 that green 
plants can manufacture carbohydrates only in the presence 
of sunlight. We also showed in Exercise 46 that oxygen is 
necessary for the germination of seeds and for the release of 
energy in living as well as in lifeless things. It is possible 
also to show by experiments the relation of moisture and 
temperature to the sprouting of seeds and the growth of 
plants. 

For the successful cultivation of individual plants or of 
crops one of the most important factors is the right kind 
of soil. This supplies to the plant the minerals necessary 
for living substance and determines to a very large extent 
the available supply of water. 

What the character and the chemical composition of 
various kinds of soils are. Year by year the scientists in 
the Agricultural Bureaus at Washington and in the various 
states are learning more and more about the marvelous 
resources in our soils and are applying this knowledge in 
helping the farmers to secure increased and more varied 
crops. The soil expert now comes to the intelligent farmer 
who has sought his advice, takes samples from the soil the 
farmer is plowing, mixes them well, and finally carries away 
some of this mixture. In the laboratory he examines it 
under the microscope to see whether the particles are fine or 
coarse. He determines whether the soil can hold a large 



250 REPRODUCTION OF LIVING THINGS 




Courtesy of Caterpillar Tractor Co., and U. S. Department of Agriculture 

Methods of cultivation of the soil 
Contrast the two horse power (right) with the fifteen horse-power tractor. 

or a small amount of water. He tests it chemically to see 
whether it has the right proportion of the chemical com- 
pounds containing the four essential elements — nitrogen, 
potassium, phosphorus, and calcium; for when any one 
of these is deficient, the crops fail to grow. 



PLANT PROPAGATION 



251 



When the examination is finished, the expert can tell the 
farmer whether he can succeed better by growing in his soil 
wheat or potatoes, corn or onions. In many cases, too, like 
the family physician in the home, the agricultural adviser 




Irrigating a farm 
The water is flowing from the larger stream between the rows of plants. 

can improve " sick " soil with nitrogen-fixing bacteria (p. 374) 
or prescribe the needed fertilizers. Often astonishing results 
come from following his counsel. 

QUESTIONS AND APPLICATIONS 

1. Locate and describe three structures seen on the concave edge of the 
bean seed. State the cause or the use of two of these structures. 

2. Name three kinds of organs that comprise the bean embryo. Give 
the number and a description of each kind. 



252 REPRODUCTION OF LIVING THINGS 

3. State the changes that take place in each of the organs you have just 
inamed, (a) in the bean seed that has just begin to sprout ; (6) in the seed- 
ling just breaking through the ground ; (c) in the fully developed seedling. 

4. Of what two parts does a corn grain consist? Which part is alive? 
What is the use of the other part ? Of what is it composed ? 

5. Name three or more parts or organs of which the corn embryo con- 
sists. State the changes that take place in each of these parts as the corn 
.seedlings develop. 

6. What is a seed? 

7. How do seeds differ, (a) in the number of cotyledons ; (6) in the 
location of stored food ? 

8. How do the embryos of seeds differ in the way they develop ? 

9. Name five conditions that are necessary for the growth of green 
plants. 

10. In what way have we already shown that two of these conditions 
.are essential for plant growth ? 

11. Name two ways in which soil contributes to the growth of plants. 

12. Describe the method employed by a soil expert to determine the 
•characteristics of soil. What advantages does a farmer derive from such 
ran examination? 

13. Describe some of the methods of increasing crop production. 

14. What is meant by plant grafting and how is it accomplished ? 

15. What are some of the advantages to be derived from grafting ? 

PROBLEM 4. HOW ARE PLANTS, ANIMALS, AND 
MAN MODIFIED? 

Introduction. In preceding pages we have discussed 
the structure, the functions, and the cultivation of seed- 
bearing plants. We are now to consider how these plants 
have become modified either in the wild state or by direct 
methods through the action of man. During the thousands 
of years since cultivation began mankind has been able to 
change plants from wild forms to those that are of great 
economic value. This has been particularly true in recent 
years through the application of scientific principles. But 
first it will be well to call attention to some of the changes 



MODIFICATION OF LIVING THINGS 



253 



that are constantly taking place in the structure of living 
things in nature all about us. 

Variations among living things. We have all heard the 
expression " as nearly alike as two peas." In reality, how- 




Variations among animals 
Enumerate as many differences as you can between the various types of horses and of 

fowls. 

ever, if our powers of observation were sharp enough, we 
should probably find that no two peas are exactly alike in 
shape, color, size, weight, and amount of stored food. The 
plants grown side by side and under the same conditions 
from any two pea seeds would also vary in height, in number 
and position of leaves, and in the number and vigor of 



254 REPRODUCTION OF LIVING THINGS 




flowers and seeds. In other words, we should bear in mind 
that every individual plant or part of a plant shows certain 
differences, or variations, from every other individual of its 
class. 

Individual animals, too, show a wide range of variations. 
If you were to study minutely a litter of puppies, or kit- 
tens, or rabbits, you 
would find, as a gen- 
eral rule, that no 
two of the animals 
would be exactly 
alike. There would 
be differences in size 
and weight, in hair 
color and length of 
legs. When the 
puppies developed 
into full-grown 
dogs, more striking 
variations would be 
noted . One or more 
of them would have 
more acute eye- 
sight, or keener 
sense of smell, or 
better running abil- 
ity than the rest. They would differ, too, in their intelli- 
gence and their response to training. So, also, if our power 
of observation were keen enough, we should be able to note 
individual differences among animals as low as frogs, fishes, 
earthworms, and even among single-celled animals. 

It is very seldom that two human beings, even so-called 
identical twins, resemble each other so closely that one can- 



'mm 





Two different thumb marks 
The two impressions at the top look much alike. 
When, however, the regions inclosed by the squares 
are magnified (in the lower figures) , it is easily possible 
to distinguish them. In the lower figure at the right 
note the pores from the sweat glands. 



MODIFICATION OF LIVING THINGS 255 

not be distinguished from the other by those who know 
them (111. below). Often there are striking differences 
among children in the same family at a given age, in the 
matter of height, weight, complexion, eye and hair color, 
muscular strength, and mental ability, and even more 
striking differences between parents and their children. 
Biologically speaking, it is not true that " all men are created 




Twin boys 

These boys resembled each other so closely that it was difficult even for their parents 

to distinguish one from the other. 

equal." Indeed, it is this wide range of individual variations 
that makes this world in which we live so interesting, and 
that makes it possible for progress to be made. Although 
scientists have devoted a great deal of study to plant, 
animal, and human variations, thus far, in spite of many 
interesting theories, we must confess that we are still in 
doubt as to the real causes of these variations. 

Overproduction of living things. A second fact that is 
evident to all of us is that many living things tend to produce 
great numbers of offspring. Suppose, for example, we con- 



256 REPRODUCTION OF LIVING THINGS 

sider the case of a vigorous pea vine, grown from a single seed 
(111. p. 222). In the course of a single season it should pro- 
duce " at least 20 pods, each containing at least 5 seeds. 
Hence at the end of one season one pea seed would, if con- 
ditions were favorable, have multiplied itself 20 X 5, or 
100 times. If each of these seeds were to be planted where 
it had plenty of moisture, light, food, air, and a favorable 
temperature, it likewise should give rise to 100 seeds, and so 
at the end of the second season we ought to have 100 X 100, 
or 10,000 pea seeds, all propagated from the original pea 
seed. Simple multiplication shows us that at the end of five 
years a moderately prolific plant like the garden pea would, 
with all conditions favorable, produce 10,000,000,000 new 
seeds. *t 

It is evident, however, that no pea vine, if left to itself, 
would be able to produce such a large number of seeds as 
we have named, for otherwise at the end of a short term of 
years there would not be room on the whole surface of the 
globe for any other kinds of plants than these. As a matter 
of fact, the number of individuals of a given kind of organism 
does not usually vary much from year to year. In the first 
place, many seeds are eaten by birds and other animals. 
Again, many other seeds are not carried to a place where 
they find all the conditions that are necessary for germina- 
tion. Still other seeds, even if planted in good soil and with 
surroundings favorable, fail to grow into mature plants. 
Because of the great losses of seeds in one or the other of 
these ways, we can get some idea of the reason why plants 
must produce a great abundance of seeds if their kind is to be 
perpetuated. 

" If the eggs of a common fly should develop, and each of 
its progeny should find the food and temperature it needed, 
with no loss by destruction, the people of a city in which this 



MODIFICATION OF LIVING THINGS 257 

might happen could not get away soon enough to escape 
suffocation from a plague of flies (111. below) . Whenever any 
insect is able to develop a large percentage of the eggs laid, 
it becomes at once a plague. Thus originate plagues of 
grasshoppers, locusts, and caterpillars." * We might also 




Courtesy of American Museum of Natural History 

A plague of flies 

In the lower part of the picture is the American Museum of Natural History. Above 

is a representation of the possible progeny of flies, ninth generation. 

call attention to the problems man has had to face due to the 
unwanted introduction into our country and the rapid repro- 
duction of the English sparrow (111. p. 424), the gypsy (111. p. 
484) and tussock moths (111. p. 482), the cotton-boll weevil 
(111. p. 518), the corn worm (111. p. 481), and the Asiatic beetle 

1 From Animal Life by Jordan and Kellogg. Used by permission of D. Appleton 
and Company, New York. 



258 REPRODUCTION OF LIVING THINGS 



(111. p. 519), and to the overrunning of Australia by rabbits 
brought in from Europe. 

" Even slow-breeding man/' says Darwin, " has doubled in 
twenty-five years. At this rate in less than a thousand 

years there would literally 
not be standing room for 
his progeny." 

The struggle for existence 
among living things. Let us 
now consider some of the in- 
evitable results of overpro- 
duction. In the first place, 
each plant is struggling to 
lift up its leaves to the light 
and air, and those that are 
most vigorous usually get 
above and shade the others 
(111. p. 259) . Again, the sup- 
ply of water and mineral 
food in the soil of a given 
area is limited ; hence, 
plants that cannot get what 
they need are dwarfed and 
finally starved to death. In 
the third place, injurious 
insects destroy an enormous amount of vegetation, the loss 
of cultivated crops alone from this cause in our country being 
estimated at $700,000,000 annually. Frosts, dry seasons, 
heavy rains, and fungous diseases (111. p. 337) are other im- 
portant factors in the life struggle of many plants. And so, 
if we were able to see what is actually going on in forest, field, 
or meadow, we should witness a life-and-death struggle for 
existence (1) between individual plants of the same kind, 




Charles Darwin (1809-1882) 

For fifty years a painstaking investigator 
of problems bearing on the theory of the 
origin of living forms. Darwin's Origin of 
Species was published in 1859. 



MODIFICATION OF LIVING THINGS 259 

(2) between individual plants of different kinds, (3) between 
plants and animals, and (4) between animals of the same or 
different kinds. 

Indeed, among animals the struggle for existence is even 
more striking and dramatic than is the case with plants. 



■Jh>:rt£ 


■1 ^ , ; ^ 




! •' Ji 


§££&■„£% 


1 ajjjfe 


', 


w# 


i ^ i 








ifr^! 


1 


| ; ?f 


■Mw 




R« fl 




if - '■ 


®m>W'^ 


h : « \ 


KlSl 


I ^'/Jl^iSBI 


' i 


y.i 


. M" s 






^' i ■ 1 


l&MP^w*V ■ 


"' fw^^S^ ■ 


l-i . Xm 


wsH 


■ * * -i 


Iff"'' ■ ^ 


: ' 5^/,* 


m 


J;;.|Pa|5?|f? ,! 




%E& '' ' ' 


«, . -4 3ra 


;?|§ 




fir ij ms 




' « US ' 1 

Mi y \ 




l^JfiC i Jill 


r • f £ 


4< ' . / •- 
r Ay * ■ 

i . y - ^ N 




IS 

• > * ■■■-, 








^%J0j&:f^ 


■■'.. 

** A 


IfeP^Sp-;^^,^^!! 


S3&* fC. A ¥^i* 


■ZJf-" 



Courtesy of Otis Shattuck, 

Struggle for existence among plants in a tropical forest 
Note the spirally twisting stems of the strangling fig, which is climbing for light. 
The tree in the center of the picture has been killed, and the one at the right is 
being strangled. Note the way the stem of the fig has pressed into the bark. 



You have all seen the hairy caterpillars that often infest our 
shade trees (111. p. 260), and have noticed the ravages they 
make. Whole branches are often stripped of their leaves 



260 REPRODUCTION OF LIVING THINGS 

in a single day, and there is doubtless keen competition 
among the individual caterpillars in their attempt to satisfy 
their voracious appetites. Those that survive are in con- 
stant danger of attack by the yellow-billed cuckoos (111. p. 
421) which seem to choose this apparently unsavory type of 
food. The cuckoos, in turn, are the prey of larger birds, of 




Caterpillars destroying leaves 
Why would there be a struggle for existence among these animals ? 

snakes, and of prowling hairy animals ; and these in their 
turn are often devoured by other animals. And so we might 
multiply indefinitely examples of the struggle for existence 
among animals (111. p. 261). 

We may now ask the question whether there is anything 
like this struggle for existence among human beings. We 
do not need to go back a great many years in the history of 
our country to see what has happened to the American 
Indians. When Europeans first discovered America, prac- 







Courtesy of American Museum of Natural History 

Struggle for existence among animals 

How many kinds of animals are shown in this museum group ? In as many cases as 

possible decide the victims preyed upon by each animal. 



262 REPRODUCTION OF LIVING THINGS 

tically the whole continent was in the possession of the Red 
Men. As settlements multiplied on our eastern coast, the 
Indians were deprived of more and more of their territory, 
were pushed farther and farther into the interior until at the 
present time scarcely more than 330,000 remain, and these 
are largely on the Indian Reservations maintained by the 
National Government. But white men, too, often engage 
in a life and death struggle that is very costly in lives lost 
and property destroyed. " The actual loss to the country of 
able-bodied men caused by the rebellion (1861-1865) was fully 
1,000,000. The total cost of the (Civil) war has been moder- 
ately estimated at $8,000,000,000. ... The property de- 
stroyed is beyond computation." 1 

In the World War (1914-1918), over 65,000,000 were actu- 
ally engaged on both sides. One of the saddest aspects of 
such struggles as these is the fact that the heaviest toll of 
death is taken from the ranks of the best of the young men 
of the world, those who are the most fitted to become the 
fathers of succeeding generations. 

" No large acquaintance with the character of warfare is 
necessary to prove that when elemental anger, hate, and fear 
prevail, civilized conventions are abandoned and the most 
savage instincts determine conduct. Homes are looted and 
burned, women and children are abominably treated, and 
many innocents are murdered outright or starved to death." 2 

Even in times of peace there is a more or less constant 
struggle for existence among human beings ; and this is 
particularly true in famines, pestilences, and business de- 
pressions with their consequent unemployment of the wage 
earners. It is probably true that overproduction and the 

1 Harper's Encyclopedia, United States History, p. 166. 

2 From Bodily Changes in Pain, Hunger, Fear, and Rage, pp. 368 and 369, by 
Walter B. Cannon. Used by permission of D. Appleton and Company, New York. 






MODIFICATION OF LIVING THINGS 263 



consequent struggle for existence among plants and animals 
results in forms of life better adapted to their surroundings. 
But is this true with human beings ? In later pages we shall 
see how mankind has gradually been substituting for re- 
morseless conflicts better ways of improving the race. (See 
pp. 279-281.) 

Survival of the fit- 
test among living 
things. We have 
seen in our study thus 
far (1) that no two in- 
dividual plants, ani- 
mals, or human be- 
ings, even of the same 
kind, are exactly 
alike ; (2) that enor- 
mous numbers of new 
individuals are pro- 
duced ; and (3) that 
there is inevitable 
competition or strug- 
gle for existence. 
The question that 
now confronts us is 
this — Which of the 
many competitors will survive in the struggle, reach matur- 
ity, and finally reproduce themselves? Obviously, those 
living organisms that vary from the rest in such a way that 
they can adapt themselves to their environment sufficiently 
well to reproduce their kind. 

Let us see, for instance, why certain weeds like the dande- 
lion are so common a nuisance on our lawns (111. above). In 
the first place, these weeds have fleshy roots that reach deep 




A dandelion plant 

Identify as many organs of the plant as you can, and 

state how each helps this weed to survive. 



264 REPRODUCTION OF LIVING THINGS 

down into the soil, thus helping the plant to get and keep 
a stock of moisture and food. In the second place, the 
reserve supply of nutrition stored in these roots enables the 
plants to put forth leaves and flowers in the early spring, and 
so to get a good start ahead of their competitors. Again, 
their short stems and tough leaves can be trampled upon 
without killing the plant. Insects and fungous diseases, for 
some reason, do not seem to attack them. And finally, 
dandelions produce a large number of tiny seedlike fruits 
(111. p. 236), each one of which is provided with a delicate tuft 
of hair which a puff of wind will carry for a considerable dis- 
tance, thus insuring a wide dispersal of its seeds. In nature, 
then, plants like the dandelion, pigweed, thistle, and other 
weeds have survived in the struggle for existence, because 
they are best fitted to their surroundings. 

Among animals those individuals of a given species that 
have keener senses of sight, smell, or hearing can more readily 
seek out their food and become aware of their enemies, while 
those less efficient perish. The rabbit with the more power- 
ful hind legs is more likely to escape the pursuing dog. The 
striking resemblance to their surroundings of the quail and 
their young and their habit of crouching when an enemy is 
near frequently enable them to elude their pursuers. Many 
animals give evidence of rather keen intelligence in securing 
their food and in outwitting their enemies. A flock of 
California woodpeckers, for instance, select a live-oak tree in 
the autumn, with their bills drill holes in the bark, and in 
each they deposit an acorn. Later, when food is scarce, they 
return to devour the acorns and the insect grubs that may 
have developed therein. The remarkable care taken of 
their young by most of the higher birds and mammals will 
be referred to later. It is evident that the young of those 
animals or of human beings that are successfully nurtured 



MODIFICATION OF LIVING THINGS 265 

and protected during their infancy are far more likely to 
survive and to perpetuate their kind. 

Thus we see how closely the four links we have studied 
thus far in the biological chain are bound together. Over- 
production inevitably leads to a struggle for existence ; 
favorable variations are likely to result in a survival of the 
fittest. This struggle, bitter and remorseless as it often 
seems to be, is doubtless for the final good of the living 
world, for by this means the weak and the inefficient are 
eliminated, and the vigorous and the successful live to 
possess the earth. 

Heredity among living things. If, however, races of 
plants, animals, and human beings are to profit permanently 
by what they have gained at such cost, these helpful varia- 
tions must be passed on to the generations that are to follow. 
This is accomplished by means of the last link in the chain 
we have been describing, namely, by inheritance. We are all 
familiar with the fact that children resemble to a considerable 
degree one or both parents, their grandparents, or their great- 
grandparents. We all know, too, that every plant and 
animal produces offspring after its own kind. By this we 
understand that something has been received or inherited 
from these ancestors which brings about these many resem- 
blances. The sum total of these various elements of inher- 
itance make the individual living organisms, whether plant, 
animal, or human being, largely what they are. That which 
is actually transmitted from forebears to offspring is the 
inheritance of the individual. When favorable variations 
occur among living things, these are likely to be passed 
on by inheritance to the generations that follow. 

Artificial selection of favorable variations. In the pre- 
ceding pages we have frequently called attention to the fact 
that plants of a given species show a tendency to vary more 



266 REPRODUCTION OF LIVING THINGS 

or less from each other. Now it has been found that when 
plants are cultivated, this tendency to vary becomes even 
more pronounced. A watchful farmer will often find that 
in his cornfield one group of individual corn plants ripens 
sooner than the rest. If, then, he wishes to sell earlier corn, 
he selects and plants next year corn grains derived from 




Courtesy of Dr. Donald F. Jones, Geneticist, Connecticut Agricultural Experiment Station 

Different types of corn 
From left to right, flint, pop, dent, flour, sweet, pod, and branch corn. 

plants that have varied in this direction. Again, he may 
notice that the corn ears on certain stalks are larger, and 
that more kernels ripen (111. above). These the intelligent 
farmer would select for seed in order to increase his crop per 
acre. Variations in many other directions might be selected 
which would add immensely to crop values. It is estimatec 
that if every farmer were to select his seed carefully, the corn 
production in the United States, which at present is between 
two and three billion bushels, in a short time would be in- 
creased 10 per cent. 



MODIFICATION OF LIVING THINGS 267 

Artificial crossing of related species. Man not only can 
secure new varieties of plants by watching for favorable 
variations and cultivating them from year to year, but he can 
also be instrumental in actually producing entirely new kinds 
of plants and animals. This process is known as plant and 
animal breeding. It depends fundamentally on the prin- 
ciples we learned in discussing the cross-pollination of 
flowers. " Few people realize how fast the vegetables, 
fruits, and flowers are changing. The wheat that goes to 
the modern steel mill in railroad car, canal barge, and ocean 
ship is not from the same varieties that the ox cart and saddle 
pack carried to the stone gristmill a few generations back. 
The housewife driving to Faneuil Hall market (in Boston) 
in 1850 with her horse and buggy would find no Green 
Mountain or Irish Cobbler potatoes, no Mcintosh or 
Delicious apples, no Elberta or Carman peaches, no Concord 
or Niagara grapes, no Howard or Chesapeake strawberries. 
Golden bantam corn and Iceberg lettuce did not exist, and 
grapefruit 1 was never seen." 2 

As an example of new fruits developed by man let us see 
how the Cortland apple was produced (111. p. 268). At the 
Agricultural Experiment Station in Geneva, New York, 
the scientific workers investigated the Mcintosh apple, 
and found that while in many respects this fruit was 
ideal, it ripened too early for winter markets and the apples 
often dropped from the trees before they were fully matured. 
Out in the West, however, grew the Ben Davis apple tree 
that bore a heavy crop, that was unharmed by heat and 
drouth, and that held on to its fruit in spite of prairie winds. 

1 Grapefruit is not an artificial cross between oranges and lemons as is commonly 
believed, but a fruit developed naturally. 

2 From Biology in Human Affairs, edited by Edward M. East, McGraw-Hill Co., 
New York. Chapter on "Efforts to Increase Food Resources" by Donald F. 
Jones. Used by permission. 




Courtesy of Dr. U. P. Hedrick, N. Y. 

The Cortland apple 
Above is the tree with its crop of fruit. Below is a single apple. 



MODIFICATION OF LIVING THINGS 269 

The problem, then, was to combine the desirable qualities 
of the two fruits, and thus to secure an almost perfect fruit. 
This is the way the Experiment Station workers went at 
their task. They removed the stamens from some of the 
opening flower buds of the Mcintosh apple tree to prevent 
self-pollination. By means of camel's-hair brushes they 
then transferred to the stigmas of the pistils of these flowers 
pollen from Ben Davis apple blossoms, and covered the 
Mcintosh flowers thus treated with mosquito netting to 
prevent the bees from bringing pollen from any other blos- 
soms. When the fruit ripened on the Mcintosh trees, the 
seeds were planted, and from the hundreds of seedling apple 
trees that grew, one was found to bear fruit which had the 
desired characteristics of both its Mcintosh and its Ben 
Davis parents. This new fruit is the Cortland apple, which 
is a rich red in color, has a delicious taste, and clings to the 
tree until the fruit can be picked. Cortland apples can be 
grown in widely separated regions of the country. 

In a similar way man has produced an astonishing number 
of new varieties of flowering plants, of grapes, peaches, corn, 
wheat, and other food products that were wholly unknown 
to our ancestors. Scientists have also learned how to 
develop cattle specially adapted to produce large quantities 
of milk, sheep specially adapted for wool or for mutton, 
horses with surprising speed records, poultry with remarkable 
egg-laying qualities, and other domestic animals of great 
use to man. All this has been accomplished in accordance 
with the known laws of inheritance. 

What are the laws of inheritance ? If you should pollinate 
the flower of a tall variety of pea plant with the pollen from 
a dwarf variety, you might expect the seeds that develop 
would produce plants intermediate in size. Up to the time 
of Gregor Mendel (111. p. 270) most scientists who thought 



270 REPRODUCTION OF LIVING THINGS 



anything about breeding were of the opinion that when- 
ever plants or animals with contrasting characters were 
crossed, the resulting offspring would be of an intermediate 
type. 

Mendel was an Austrian monk who became interested in 
cross-pollinating the flowers of various kinds of garden peas 
and then making accurate observations of the results. 

His experiments were carried 
on in the monastery garden 
at Briinn, near Vienna. In 
one plot of the monastery 
garden at Briinn there were 
plants of a tall variety and 
in an adjoining plot plants 
of a dwarf variety. Mendel 
took pollen from the dwarf 
variety and placed it on the 
stigmas of the flowers of the 
tall variety of plants, having 
first taken the precaution of 
removing the stamens from 
the flowers of the " tall " pea 
plants to prevent self-polli- 
nation. He let the seeds 
ripen and then planted them 
the next spring. Every 
plant that grew from these seeds was " tall " ; not a " dwarf 1 
nor an intermediate plant appeared. He then allowed the 
plants to self -pollinate, and when the seeds were ripe they 
too were gathered and planted the following spring. To his 
surprise a number of " dwarf " plants appeared. About one 
fourth of the entire number were " dwarf," the remaining 
three fourths being " tall." 



















jjffltw 




1 




















3H^H 










, 


tr*-'"*- 








^^■ISiill 










]r WM&*ff': 





















Couriesy of American Museum of Natural History 

Gregor Mendel (1822-1884) 
How are Mendel's laws of inheritance 
important to plant and animal breeders ? 




Courtesy of American Museum of natural History 

Three generations of the garden pea 

Upper row, left, yellow peas (light) ; right, green peas (dark). Second row, one 
pea pod, result of crossing a plant having yellow peas with one having green peas. 
Which is the dominant character, yellowness or greenness? Third row, second 
generation. In what proportion do the green peas appear as compared with the 
yellow ? Fourth row. How is Mendel's law of segregation shown in this generation ? 



272 REPRODUCTION OF LIVING THINGS 

He likewise made similar crossings using other pairs oj 
characters. When he crossed, for instance, the blossoms oi 
pea plants bearing yellow seeds with the pollen of plants 
that bore green seeds, only plants with yellow seeds appeared 
in the first generation ; but both yellow and green in the 
second generation. He crossed smooth with wrinkled, purple 
flowered with white — each time with a similar result. 

It was apparent, then, that when these individual con- 
trasting characters met in the reproductive or germ cells of the 
same plant, only one of them — tall, yellow, smooth — 
came to expression in the mature plant. The other charac- 
ter did not show at all in this first generation. It seemed 
to have disappeared, but it made its appearance in the next 
generation ; hence it must have been simply hidden or sup- 
pressed in the first crossing. Mendel called the trait which 
appeared the dominant and the suppressed trait the recessive. 
The plants which produced only one kind of offspring, 
for example just " tall," he called the pure type; those 
which produced two kinds, both " tall " and " dwarf," 
he called hybrid plants. 

He experimented still further by permitting the flowers 
of each plant of the second generation to self -pollinate. 
Every plant showing the recessive trait produced descen- 
dants every one of which was recessive like itself. It was 
therefore a pure type. About one third of those showinj 
the dominant trait produced descendants like themselves 
that is they too were of a pure type. The remaining twc 
thirds showing the dominant characteristic produced de- 
scendants some of which showed the dominant trait anc 
others the recessive ; in other words they were hybrids. 

Mendel reported his results and conclusions in a papei 
read before the scientific society of Briinn in 1865. Th< 
next year the paper was published, but the scientific work 




jy 




RR 




F, 



R 



DD DR DR RR 



Courtesy of American Museum of Natural History 

Two generations of the fruit fly 
Upper row, DD, fruit fly with normal wings. RR, fruit fly with vertical (rudi- 
entary) wings. Fi, first generation, result of crossing fruit fly having normal wings 
with fruit fly having vestigial wings. How is Mendel's law of dominance illustrated 
this generation? F 2 , second generation. How is Mendel's law of segregation 
llustrated in this generation ? What is the proportion of pure types to hybrid ? 



274 REPRODUCTION OF LIVING THINGS 

did not realize its significance. In 1900, three European 
botanists working independently rediscovered what are now 
known as Mendel's laws. Then MendePs paper was found. 
Experimenters on plants performed anew Mendel's careful 
experiments, and confirmed his results. Other biologists 
worked with animals and found that Mendel's laws of 
heredity applied also to them. For instance, animal breeders 
found that gray color dominated all other colors in horses, 
pacing dominated trotting. In dogs any one color domi- 
nated mixed colors ; in guinea pigs black dominated white. 

Let us now consider some of the practical applications 
that have been made of these laws that Mendel discovered. 
A few years ago wheat crops in the West were being destroyed 
by a fungous disease known as wheat rust (see p. 338). 
In a badly infected field one plant was found which appeared 
to be perfectly healthy ; that is, it was evidently immune 
to the disease. This plant was crossed with an infected 
plant, but none of the descendants escaped the disease. 
If the plant breeder had not known Mendel's laws, he 
probably would have given up the experiment as hopeless. 
These laws of heredity, however, had taught him that the 
immune trait might be recessive, and though hidden in one 
generation might appear in the next. He decided to plant 
the seeds he had secured by the crossing. One fourth of the 
new plants thus obtained were immune ; three fourths were 
susceptible. Immunity to wheat rust, therefore, was 
evidently a recessive character. The immune plants were 
preserved, their seeds were collected, and a strain of wheat 
immune to wheat rust was developed. In the same way 
breeders have crossed plants having certain desirable anc 
certain undesirable traits and by crossing and recrossinj 
have succeeded in securing all the desirable and none of th( 
undesired traits in one individual plant. 



MODIFICATION OF LIVING THINGS 275 

Because of the knowledge of Mendel's laws plant and 
animal breeders to-day carry on their experiments with a 
directness and a feeling of certainty. Results which appear 
disappointing and which probably would have put an end 
to experiments in former days are now recognized as steps 
in a procedure which if carried out will eventually give the 
result desired. 

Briefly, then, the laws of inheritance which Mendel dis- 
covered are : (1) The law of dominance. Whenever two con- 
trasting characters are brought into combination by crossing 
two plants or two animals, one of these characters may be 
dominant over the other, the recessive character. (2) The 
law of segregation. Segregate means to separate. Thus 
when the " tall " pea plants and the " dwarf " pea plants 
were crossed, the seeds formed produced plants expressing 
only one character, tallness. When, however, these plants 
were self -pollinated, the seeds that resulted brought forth 
both tall and dwarf plants. That is, in the second genera- 
tion, segregation or separation of the recessive character from 
the dominant occurred. In the same way the recessive 
character of immunity to wheat rust was segregated in the 
second generation from the dominant character suscepti- 
bility to the wheat rust. 

Students of human heredity have studied records of 
families and have found that Mendel's laws also apply in 
this field of biology. Thus brown eyes have been found to 
be dominant over blue eyes, curly and brown hair is domi- 
nant over straight and red hair, normal mind over feeble 
mind. Consequently it is possible to predict the chances 
of the appearance in a given generation of certain characters 
that have been studied. 

The great importance of a good heritage. In this unit we 
learned that each individual in the successive generations 



276 REPRODUCTION OF LIVING THINGS 

of higher living things is formed from a fertilized egg cell. 
We found that for this reason the offspring of plants and 
animals resemble the parent organisms from which the sperm 
cells and egg cells came. " Like produces like " is a general 
rule that applies throughout the world of living organisms. 
Race horses are descended only from other race horses. " It 
is blood that tells," whether in race horses or in human 
beings. 

" The biologist holds," says Dr. Walter, " that, although 
what an individual has and does is unquestionably of great 
importance, particularly to the individual himself, what he is, 
in the long run is far more important. Improved environ- 
ment and training may better the generation already born. 
Improved blood will better every generation to come." l We 
are now to turn our attention to certain family histories, in 
which we shall find it strikingly true that heritage plays a 
dominating part. 

Heritage in the Kallikak family. An absorbing tale of 
heredity 2 was worked out after long and patient investigation 
by Dr. Henry H. Goddard while he was Superintendent of 
the Training School for the Backward and Feeble-minded at 
Vineland, New Jersey. To that school in 1897 came a seven- 
year-old girl, who had been born in an almshouse. She had 
not done well in school and was difficult to control ; hence 
she was put in the Vineland School. 

When Dr. Goddard began to study the ancestry of this 
little girl, he soon found great difficulty, for apparently her 
relatives were of two entirely different types ; namely, some 
who were well-to-do and highly intelligent, and some who 
were poor and feeble-minded. At last the key to the puzzle 

1 From Walter, H. E. , Genetics. Used by permission of The Macmillan Company, 
publishers. 

2 The Kallikak Family, by Dr. Henry H. Goddard. The Macmillan Company. 






UjU /Vorme/ man 
\y A/or ma/ woman 
13 Feeb/e-minded man 



D /735 



■® 



DJ765 



Feeb/e-minded woman 



-® 



m 



Eh 



Undetermined man 



d inf Died in infancy 



D /770 ^ 
Name/ess \ 

feeb/e-minded girt ^ 



<S) 




Norma/ wife 
After the Revo/utton /j-v 









« 


















1 


c 


5 


to 


1 




5 


id 


<; 


«1 


V 






'*) 


o 


N 


<•> 




* 


$ 


<S 


§ 


$ 


^ 



©--HHffi)® ®®G3® 



Justin 



m 



<8> 



Gg- 



<S) 



Deborah 



ED — I — ® 



E] 



The Kallikak family 



Of the 480 descendants of this branch 
of the family 143 (21%) were feeble- 
minded ; only 46 (9%) were normal ; of 
the rest 189 (68%) are still undeter- 
mined. 24 were confirmed alcoholics ; 3 
were criminals; 3 were epileptics; 82 
died in infancy ; 41 were degenerate. 



Of the 496 descendants of this branch 
of the family, none were feeble-minded, 
and all were good citizens. Among them 
were doctors, lawyers, judges, educators, 
traders, landowners — men and women 
prominent in every phase of social life. 
Only 2 were alcoholic. 



278 REPRODUCTION OF LIVING THINGS 

was found way back in the time of the Revolutionary War 
in the person of a man to whom Dr. Goddard gave the 
fictitious name Martin Kallikak, Senior. (Kallikak is a 
combination of two Greek words that mean good-bad.) 

As far as is known (111. p. 277) Martin Kallikak' s ancestors 
were all normal men and women. But during the Revolu- 
tionary War he became the father of a boy whose mother 
was a feeble-minded young woman. This son, Martin 
Kallikak, Junior, inherited the feeble-mindedness of his 
mother. He married, however, a woman who was more or 
less normal. Of the ten children of these two parents 
(father, feeble-minded; mother, normal), two died in in- 
fancy, five were feeble-minded, the mental condition of one 
could not be determined, and only two were thought to be nor- 
mal! A great deal has been learned regarding the history 
of 480 of the descendants of Martin Kallikak, Senior, and 
the feeble-minded mother ; some of the facts relative to their 
physical and mental condition are stated on the left side of 
the chart (p. 277). With such an ancestry as that repre- 
sented on the chart, what possible success could be attained 
by poor little Deborah ! Born in an almshouse, with feeble- 
minded ancestors through at least six generations, she was 
brought to an institution for the feeble-minded at seven, 
there to remain, it is hoped, as long as she lives. This in 
brief is the dark side of the Kallikak story. 

Let us turn now to another phase of this study in heritage. 
At the close of the Revolution Martin Kallikak, Senior, 
married a Quaker girl of good ancestry and lived a respectable 
life after the traditions of his forefathers. Of this marriage 
seven children were born (see right side of the chart), and in 
all 496 descendants have been traced. All of these have been 
normal, good citizens except two, and of these not one was 
feeble-minded. 



MODIFICATION OF LIVING THINGS 279 

In both of these lines of descent, it should be remembered 
that the original ancestor (Martin, Senior) is the same. 
The descendants of the two mothers have been traced in 
every kind of environment, and each of the two lines of chil- 
dren has always shown the characteristics of their respective 
mothers. The same would have been true had the father 
been feeble-minded. Hence, we are forced to conclude that 
heritage was the controlling factor in the formation of their 
traits of character, and we are compelled to believe that 
feeble-mindedness is an hereditary characteristic. 

What should be done with the feeble-minded. After a 
careful reading of the preceding paragraphs, it will hardly be 
necessary to emphasize the fact that feeble-minded, criminal, 
and diseased individuals, like those in the Kallikak family, 
should be discovered early in life. They should be cared for 
at public expense in State institutions and thus should be 
prevented from transmitting to other generations their 
physical, mental, and moral weaknesses. Dr. Hart, formerly 
Director of the Department of Child Helping of the Russell 
Sage Foundation, after a long experience in dealing with 
these problems, assures us that a few generations only 
would be required to eliminate from human society the 
feeble-minded and the socially diseased if mankind would 
only adopt the sane measures just suggested. Certain it is 
that every right-minded individual should avoid marrying 
into a family in which there is ancestral feeble-mindedness 
and should gladly cooperate with clergymen and others who 
refuse to join in marriage those who cannot furnish physical 
— and mental — health certificates signed by reliable phy- 
sicians. 

Heritage in the Jonathan Edwards family. We now turn 
to a study of the lasting benefit that comes to the individual 
and to the race from children born of vigorous and highly 



280 REPRODUCTION OF LIVING THINGS 



intelligent parents. In striking contrast to the story of the 
branch of the Kallikak family descended from the nameless 
feeble-minded mother is the family history of Jonathan 
Edwards (111. below), the most eminent preacher and thinker 
of New England in the early days of its history. Dr. 
Edwards had a remarkable ancestry ; he married a wife 

(Sarah Pierpont) with an 
equally remarkable heri- 
tage ; and of his descend- 
ants Dr. Winship speaks 
as follows: "1394 of 
these descendants were 
identified in 1900, of 
whom 295 (more than 
one out of every five) 
were college graduates ; 
13 were presidents of 
our greatest colleges, be- 
sides many who were 
principals of other im- 
portant educational in- 
stitutions ; 60 were phy- 
sicians, many of whom 
were eminent ; 100 and 
more were clergymen, missionaries, or theological professors ; 
75 were officers in the army and navy ; 60 were prominent 
authors, by whom 135 books of merit were written and 
published and 18 important periodicals edited ; 33 American 
states and several foreign countries have profited by the 
beneficent influence of their eminent activity ; 100 and more 
were lawyers, of whom one was our most eminent professor 
of law (Professor Woolsey of Yale) ; 30 were judges ; 80 held 
public office, of whom one was Vice President of the United 




Jonathan Edwards 



MODIFICATION OF LIVING THINGS 281 

States (Aaron Burr) ; 3 were United States Senators ; several 
were governors, members of Congress, framers of state consti- 
tutions, mayors of cities, and ministers to foreign courts ; one 
was president of the Pacific Mail Steamship Company ; 15 
railroads, many banks, insurance companies, and large indus- 
trial enterprises have been indebted to their management. 
Almost every department of social progress and of public wel- 
fare has felt the influence of this healthy, long-lived family. 
It is not known that any one of them was ever convicted of a 
crime." ] Any descendant of Jonathan Edwards may well be 
proud that such blood flows in his veins. Few if any families 
have contributed more to our national welfare than has this. 

The importance of a wise choice in marriage. One fact 
should be especially emphasized in the study of the Edwards 
family ; namely, that in each of the various marriages both 
parents were individuals with healthy bodies, well-trained 
minds, and high moral characters. A young woman who 
wishes to marry a man for the sake of reforming him may 
possibly succeed in so doing although there is little evidence 
to show that this is probable. But even though she may 
succeed, she runs a grave danger of having her children 
burdened with the taint of disease or the traits of character 
which injured the father. 

A great movement of the present day is that known as 
Eugenics, which is thus defined by the late Sir Francis Galton, 
who was so instrumental in its founding : " Eugenics is the 
science which deals with all the influences that improve the 
inborn qualities of the human race ; also with those that 
develop them to the utmost. " We are slowly learning that 
any permanent improvement of the human race can come 
only as a result of better heritage. 

1 Quoted from "Jukes-Edwards," by Dr. A. E. Winship. Used by permission of 
New England Journal of Education. 



282 REPRODUCTION OF LIVING THINGS 

QUESTIONS AND APPLICATIONS 

1. Name the four links in the biological chain. 

2. In what respects may pea seeds and pea plants vary? 

3. What variations would be likely among the offspring of domestic 
animals ? 

4. Make a list of the variations you have noted among the children in 
your own family or in the families of your acquaintance. 

5. Study the illustration on page 618 and enumerate the striking 
differences in the appearance of the four Taft brothers and in their con- 
tributions to human welfare. 

6. Study the illustration on page 344 and state the possible multipli- 
cation of bacteria during 24 hours. What can you say as to the possible 
overproduction of peas and house flies if there were no checks to multipli- 
cation ? 

7. Give as many reasons as you can why a struggle for existence must 
inevitably follow this enormous overproduction of plants and animals. 

8. In what ways may this overproduction contribute to plant and 
animal improvement in nature ? 

9. Discuss the struggle for existence among human beings (a) in times 
of war; (6) in times of peace. How may this struggle be (a) advanta- 
geous; (b) injurious? 

10. Give as many reasons as you can why the dandelion plants are such 
troublesome weeds. 

1 1 . Why have plants introduced from Europe often become troublesome 
weeds here ? Name animals thus introduced that have become pests. 

12. What is meant by heredity? Why is this a very important factor 
in biological development ? 

13. How does a successful farmer make use of favorable variations 
among plants and animals ? 

14. Name some of the valuable plant products which have become 
available largely through plant breeding. 

15. Describe the steps that were taken by scientists to produce the 
Cortland apple. What improvements in this fruit resulted from the 
crossing of the Ben Davis and the Mcintosh apples ? 

16. Name some types of animal that have been produced by applying 
scientific principles. 

17. Bearing in mind what you have learned state why the following 
animals are fitted to survive : (a) the tiger in India ; (b) the rattlesnake in 



THE HISTORY OF LIVING THINGS 283 

Arizona ; (c) the English sparrow in cities ; (d) the thistle in dry pastures ; 
(e) the mosquito in swamps. 

18. Give an account of Gregor Mendel and of his experiments with 
pea plants. 

19. What is meant by dominant and recessive characters? Show how 
these terms apply in the breeding of peas. 

20. Is immunity to rust in wheat a dominant or a recessive character? 
How was a strain of wheat immune to wheat rust developed ? 

21. What is the law of dominance? 

22. What is the law of segregation? Show how this law was applied 
in securing a strain of wheat immune to rust. 

23. What striking facts as to the family history of the Kallikaks were 
learned by Dr. Goddard? What must be done if mankind would check 
the increase of f eeble-mindedness ? 

24. What remarkable contributions to American life have been made 
by the descendants of Jonathan Edwards and Sarah Pierpont? What 
possible explanations of these contributions can you suggest ? 

25. Look up the family history of some of the following Americans: 
the Herreshoffs (builders of the racing yachts that have kept the " America 
cup" on this side of the Atlantic), the Roosevelts, the Lincolns, the Lees. 
What evidence do you find for the statement "It is blood that tells " ? 

26. Since no two of us, even in the same family, have equality of heri- 
tage and of environment (or opportunity), what is the wise and courageous 
attitude for each one of us to take ? 

PROBLEM 5. HOW DO WE LEARN THE HISTORY OF 
LIVING THINGS? 

Prehistoric plants and animals. In the preceding chapters 
we have been considering plants, animals, and human beings 
only as they exist to-day. But were we to limit our study to 
the living forms we see about us, our ideas of biological 
history would be very incomplete, for each of these plants 
and animals has a long, long history that extends back 
through the ages. This history the paleontologist (pa/le- 
6n-tol'6-jist, student of ancient forms of life) finds written 
in the rocks or in deposits of sand and mud. It has taken 



284 REPRODUCTION OF LIVING THINGS 



years of patient study by a multitude of trained investigators 
to decipher the writing of this past history ; but the record is 
becoming fairly complete. Let us make a brief study of the 
way in which this history was written and of some of the 
lessons that it teaches. 

In all bodies of water there is a certain amount of sediment 
that has been carried from the soil over which the water has 

passed on its way 
through brooks and 
rivers to the ocean. 
In the course of time 
this sediment settles 
on the bottom and 
may become quite 
thick. As you prob- 
ably know, the bed 
of the Mississippi 
River has been con- 
stantly rising over 
many years on ac- 
count of this con- 
tinuous deposit from 
streams that flow 
into it from large areas of country. You doubtless know 
that the harbors at the mouth of rivers must regularly 
be dredged to remove the soil that has been deposited, thus 
impeding navigation. 

In ages past soil or sand or mud was deposited beneath 
the waters that covered portions of the earth. This process 
must have continued over a very great number of years. 
Thus the deposits came to be hundreds and even thousands 
of feet in thickness. The enormous pressure exerted by this 
accumulation of soil washed down from the mountains 




Courtesy of American Museum 

Fossil corals 



Natural History 



THE HISTORY OF LIVING THINGS 285 



changed the lower layers of sand or mud into rocks. Since 
the rocks formed this way are in layers, they are called 
stratified rocks (from Latin 
words meaning layer and make). 

The animals and plants that 
existed in earlier times that 
were caught in this mud or 
that died at the bottom of the 
water would finally be buried 
and thus remain for our obser- 
vation millions of years after. 
It is no wonder, then, that pale- 
ontologists, on breaking open 
these stratified rocks, often find 
within them the remains (111. 
p. 284) or impressions (111. at 
right) of those earlier plants and 
animals. These forms are 
known as fossils. The word 
fossil really means " something 
dug up." 

The fossils found in neighbor- 
ing locations often resemble one 
another more closely than do 
those of widely separated re- 
gions. As one would expect, 
the plants and animals that are 
represented by the fossil re- 
mains in the recent periods of the earth's history often re- 
semble more or less closely the living forms of to-day. For 
example, the redwoods (sequoia) of next to the last geological 
age resemble the sequoias growing to-day in California (111. 
p. 13), but nowhere else. But as the scientists investigate 




American Museum 
Natural History 



A fossil leaf 



286 REPRODUCTION OF LIVING THINGS 

the stratified rocks formed millions and millions of years ago, 
they find countless evidences of living things very different 
from those living now ; for example, reptiles of enormous 
size (111. below). Many forms are more primitive in their 
structure than their modern descendants. In the case of 




Courtesy of American Museum of Natural History 



A prehistoric reptile 
Compare the size of this reptile with that of the men. 

animals like the horse (111. p. 288) and the camel it has been 
possible to reconstruct from fossil forms an almost complete 
history of the gradual development of these animals through 
succeeding geological ages. 

Another very striking fact has been discovered by scien- 
tists, namely, that in the course of the development of an 
individual plant or animal from egg cell to adult it often 



THE HISTORY OF LIVING THINGS 



287 



passes through stages more or less closely resembling the 
various ancestors from which the individual was descended. 
For example, in the course of the development of animals as 
high in the scale of life as the birds and the mammals we 
find distinct evidence of 
the presence of gill-slits, 
resembling those found 
in fishes. Gills would, 
of course, be useless to 
an animal that lived out 
of water. Zoologists 
consider this fact as evi- 
dence that these modern 
living things must have 
had, ages ago, fish-like 
ancestors. The devel- 
opment of the heart 
through the embryo 
stages of higher animals 
teaches us a similar 
lesson. First, there is 
a single auricle and a 
single ventricle resem- 
bling those of a fish 
heart (111. p. 454), and 
only gradually, as the 
animal approaches ma- 
turity, does each heart 
chamber become divided 
to form the two auricles and the two ventricles of the bird 
or the mammal. 

This story which paleontology teaches stretches over 
countless millions of years. During these long periods the 




Courtesy of American Museum of Natural History 

Prehistoric plants 

Plants like these helped to form the coal with 

which we heat our houses. 






288 REPRODUCTION OF LIVING THINGS 



earth's surface has passed through great changes. For 
instance, in earlier days a considerable area of our own 
country was covered by deep layers of ice, known as con- 
tinental glaciers. These successive changes in climate had 
profound effects on the various living forms which then 
existed. We learned on pages 252-275 that the plants and 




Restoration by Charles R. Knight. Courtesy of American Museum of Natural History 

A prehistoric horse, Eohippus 

Observe the four toes of each front leg. These horses lived in western North America. 

They were about twelve inches in height. 

animals of to-day are continuing to change in nature, and 
that man can often modify the living things he has found 
useful to suit his needs. 

The history and distribution of man. Paleontology also 
teaches us that man himself had ancestors that were far 
more primitive in their structure and in the way in which 
they lived. Many of the implements they used in their daily 
life have been discovered in caves, or in the deposits of sand 
and mud. All these evidences show that man, too, has had a 



Neolithic Implements' 

{drawn to 
dxfferuui 
vales) 



and. horn 
axe and 




of polished stone 



Flint 

arrow-heads 



<T.T?.1*. 



From H. G. Wells, " The Outline of History 

Stone Age tools and weapons 



290 REPRODUCTION OF LIVING THINGS 

long history. From earlier times to the present there have 
been not only changes in the bodily structure of mankind, 
such as the shape of the skull, relative length of arms, and 
other changes of structure, but also great changes in what is 
known as human culture. For example, man in very early 
times made his rude implements by chipping stones (111. 
p. 289) . This was in the Old Stone Age. At a later time man 
learned to make and fashion bronze. This was the Bronze 
Age. Later still came the ages of iron, steam, and electricity. 
It has been estimated that the human race now numbers 
about two billion individuals. In different regions of the 
world are races that differ widely in their bodily appearance, 
degree of culture, and their mode of life. For example, 
there are the Pygmies of equatorial Africa, the shortest of 
known races, who are timid and shy and live in the recesses 
of the forest. In South Africa are the Bushmen ; their 
chief weapons are the bow, with poisoned arrows, and they 
possess only the rudest huts and utensils. In the cold 
regions of the north the Eskimos live in small family or 
tribal groups without chiefs, and get their food by hunting 
and fishing. The North American Indians represent a 
somewhat higher stage of civilization than the Eskimo, at 
least since they came under the influence of European colo- 
nists. Finally, we are more familiar with the characteristics 
of the Negroes, the Mongolians (Chinese and Japanese), and 
the Caucasians. It is evident, then, that man has been able 
to adjust himself to widely varying conditions of climate, 
from the snows of the Arctic to the heat of the tropics. 

QUESTIONS AND APPLICATIONS 

1. What is meant by stratified rocks ? How are these rocks formed ? 

2. How do you account for the presence of remains of plant and animal 
forms imbedded in the rocks ? What is a fossil ? 



THE HISTORY OF LIVING THINGS 291 

3. Name some ancient forms that resemble those in existence to-day. 

4. Show what changes have taken place in the structure of the horse 
during millions of years. Why has it been possible to reconstruct the 
past history of the horse ? 

5. Give some examples to show that living organisms in the course of 
their development have stages in which they resemble their probable 
ancestors. 

6. What changes have occurred on the earth that may have helped to 
bring about modifications in the structure of living things? 

7. What is there to show that the human race has had a long history? 

8. What are some of the evidences to show that man has passed through 
various phases of culture? 

9. What is meant by the Old Stone Age and the Bronze Age? 

10. How do some people of to-day differ from ourselves in their bodily 
appearance and culture? 

11. What method of regulating the heat of the body does man possess 
which enables him to adjust himself to the extremes of heat in the Arctic 
regions or in the tropics ? 

12. Give examples to show why it is not possible to classify scientifically 
animals as wild and tame (domesticated) . Suggest reasons to account for 
the disappearance from the earth of huge monsters like the giant sloth. 

13. How do you explain the disappearance of the American bison (or 
buffalo) except for those that have been preserved in national parks ? 



UNIT VIII. PLANTS AND HUMAN WELFARE 

PROBLEM 1. HOW ARE PLANTS CLASSIFIED? 
Common Methods of Classification 



Herbs, shrubs, and trees. One way of classifying the com- 
mon plants with which we are most familiar is that of calling 

them either herbs, shrubs, 
or trees. This classifica- 
tion is based upon the 
general similarity in size, 
form, and texture of the 
plants which are assigned 
to each group. Thus 
when we think of a tree 
(111. at left), we have in 
mind a plant which, when 
mature, is of large size, 
with a single woody 
trunk and branches. 
This trunk may extend 
up nearly to the top of 
the tree, as in the case 
of the pines and spruces, 
or some distance above 
the ground the trunk may 
divide into branches, as 
in the elms and maples. 
A shrub, on the other hand, is usually of smaller size, 
even when fully grown, than is a tree; it commonly does 

292 







^fr 


fSrfjX^^l^^m r " 




jfef% 


Ijfc v1 Vw 


p^%* 


iFm B|L ^J 




{fjflJIB ' I] 




• 


pteM 





Courtesy of Brooklyn Botanic Garden 

An elm tree growing in the open 

How would life conditions for this tree differ if 

it were growing in a dense forest ? 



PLANT CLASSIFICATION 



293 



not have a single trunk, but several woody stems which 

often start from the ground level, as in the lilac, rose, and 

witch-hazel. Both 

shrubs and trees are 

alike in that their 

stems and branches 

do not die down to 

the ground at the 

end of the season. 

An herb, as the 
term is used in plant 
biology, is a plant of 
relatively small size, 
with comparatively 
little woody material 
in its stem, which 
dies down to the 
ground level at the 
close of each season. 
Such are beans (111. 
p. 16), corn (111. 
p. 231), and morn- 
ing glories. The 
roots or the under- 
ground stems of 
some herbs — for ex- 
ample, dahlias, car- 




Young seedling 



Section of swollen root 
The carrot plant 



rots (See 111.) and ^**y can cam) t Plants grow and mature their seeds so 

rapidly the second year ? 

parsnips — remain 

alive ready for growth the next year. These facts suggest 

another method of classifying plants, namely, as : 

Annuals, biennials, and perennials. When a plant at- 
tains its maturity in one season's growth and then dies, as 



294 PLANTS AND HUMAN WELFARE 

do beans, corn, and morning glories, it is called an annual. 
Many plants which have fleshy roots, like the beet, carrot, 
and parsnip, do not produce flowers and seeds until the 
second year. During the first season after the seed is 
planted the food manufactured in the leaves passes down 
the plant and is stored beneath the ground. At the end of 
the season the stems and leaves above ground die ; but if 
this root remains in the ground or is planted the next season, 
stems, leaves, and flowers develop rapidly, and finally seeds 
are formed, the food stored up the preceding season being 
drawn upon for the development of these parts. Plants 
which have a life history like this and which live for two years 
only are called biennials (Latin, bis = two + annus = year). 
Perennials are plants that live year after year. Hollyhocks 
and dahlias, for instance, store food in fleshy roots year 
after year, while the parts above ground die, as in the case 
of beets and carrots. Other perennials, like trees and shrubs, 
lose only their leaves at the end of each season. 

Deciduous and evergreen trees and shrubs. Trees and 
shrubs may be classified as evergreen or deciduous (de- 
sid'u-#s). Since the leaves of pines, spruces, and hemlocks 
remain green and attached to the stem during several seasons, 
these plants are known as evergreens. Certain shrubs (rhodo- 
dendrons, arbutus, holly, and wintergreen, for example) also 
keep their green leaves throughout the winter, and so in a 
sense they may be regarded as evergreens. Maples, elms, 
horse-chestnuts, and innumerable other trees and shrubs, on 
the other hand, shed their leaves in autumn ; they are there- 
fore deciduous (Latin, de = from + cadere = to fall). 

Scientific Method of Classification 

Scientific classification of plants. The various methods 
of grouping plants that we have thus far considered do not 



PLANT CLASSIFICATION 295 

indicate real relationships among plants, for these schemes 
call attention only to certain superficial resemblances and 
differences in form, or size, or habit. Scientific classifica- 
tion seeks to bring together into a given group all of the 
plants that are related to each other ; that is, those which are 
probably descended from common ancestors. 

It may well be asked , how one may tell whether certain plants 
are related to each other or not. There can be no doubt that 
two individuals are closely related when they are so nearly 
alike in structure that one can scarcely distinguish one from 
the other. You have doubtless seen twin children that were so 
nearly alike that their own parents could scarcely tell one from 
the other. Have you not also seen two plants that seemed so 
exactly alike that you would be sure they must be the same 
kind of plants and consequently have the same name ? 

Spermatophytes. Individual plants, on the other hand, 
may be very different in structure in many respects and 
yet have certain fundamental characteristics which make 
it seem probable that these two kinds of plants have a com- 
mon ancestry even though their relationship is not close. 
Thus though a tulip plant and a maple tree are very different 
from each other in many respects, still they have fundamental 
characteristics in common which are shared by a great many 
other kinds of common plants. They both develop flowers in 
which seeds are formed. All the plants that produce seeds 
are grouped together under the subkingdom seed-bearing 
plants or Spermatophytes (spur'md-to-fits'). 

Pteridophytes. A second group of plants includes the 
ferns and their relatives. These plants produce neither 
flowers nor seeds and yet in some respects they are like the 
seed plants in structure. They have true roots, stems, and 
leaves, each with conducting tissues that are similar to the 
fibrovascular bundles of the seed-producing plants. The 



296 PLANTS AND HUMAN WELFARE 

ferns and their allies are placed in the subkingdom Pterido- 
phytes (ter'i-do-fits') or fern plants (111. p. 324). 

Bryophytes. A third group of plants includes the mosses 
and their relatives. These plants lack the fibrovascular 
conducting tissues present in the two preceding groups. 
While they have what appear to be stems and leaves, never- 
theless these parts are much simpler in structure than the 
leaves and stems of the seed plants and ferns. Their re- 
productive organs and other parts indicate that these plants 
are related. Hence the mosses are placed in a subkingdom 
Bryophytes (bri'6-fits) or moss-like plants (111. p. 329). 

Thallophytes. The fourth group of plants includes those 
that are even simpler in structure than the mosses. Some 
of them are bacteria, molds, mushrooms, and seaweeds (pages 
330-377). The plants in this group have no parts that are at 
all structurally like stems or leaves. They are consequently 
placed in the fourth subkingdom Thallophytes (thal'6-f its) . 

Most of our attention thus far has been given to the first 
or the most highly differentiated group, namely, the seed- 
producing plants. This group embraces the herbs, shrubs, 
and trees with which we are most familiar. We should 
bear in mind, however, that many plants, like the palm and 
rubber plant, which do not produce flowers in our climate, 
develop flowers, fruits, and seeds when they are growing 
in their natural homes. Other plants with inconspicuous 
flowers (for example, grasses, elms, and pines) also belong 
to this great group of seed-producing plants. 

QUESTIONS AND APPLICATIONS 

1. What are the principal differences between the plants that are called 
herbs, shrubs, and trees? 

2. Make lists of plants with which you are familiar under the headings 
of herbs, shrubs, trees. 






FLOWERING PLANTS AND HUMAN WELFARE 297 

3. How are annuals, biennials, and perennials distinguished ? 

4. Make a list of annuals, biennials, and perennials that you have seen 
growing in gardens. 

5. Make lists of deciduous and evergreen trees and shrubs that you can 
recognize at sight. How can you distinguish one of these groups from the 
other ? 

6. What is the basis for the scientific classification of plants ? 

7. Name the four great groups to which plants may be assigned. Name 
several plants that belong to each group. 

8. What are the prominent characteristics of each of the four great 
groups or subkingdoms of plants? 

PROBLEM 2. HOW ARE FLOWERING PLANTS RELATED 
TO HUMAN WELFARE? 

Different points of view in studying plants. Thus far 
we have considered the principal functions of plants and 
have observed some of their adaptations of structure for 
performing these functions. We have seen that, in order 
to live and grow, plants must manufacture, digest, and 
transport food and must breathe and carry on oxidation. 
In order to perpetuate their species, they must reproduce 
their kind. These are the biological functions of plants. 
We have discussed the various methods of plant classifica- 
tion. Plants may also be studied in their relation to human 
welfare. 

Uses of Plants for Foods, Beverages, or Medicines 

Cereal foods. These foods include wheat, corn (111. p. 231), 
oats, barley, rice, and others. All these belong to the grass 
family, which includes more than 3500 species. The stems 
and leaves of these plants and of other grasses, when dried, 
form a great part of the winter supply of food (fodder) for 
plant-eating (herbivorous, her-bfv'6-rus) domestic animals. 
To man these cereal crops are most important because of the 



298 PLANTS AND HUMAN WELFARE 

valuable grains (fruits with a single seed) that develop from 
flower clusters at the top or along the sides of the stems. 
These grains furnish generous supplies of starch and to a 
less extent proteins, fats, and mineral matter. When they 
are dried and ground, they form flours or meals of various 
kinds, which, with the possible exception of corn meal, may 
be kept indefinitely if dry. 

These grain crops have been cultivated so long by man 
that scientists are not certain from what wild ancestor among 
the grasses any one of them has sprung. Wheat, for ex- 
ample, has been found in the pyramids of Egypt ; it must 
have been put there more than 3000 years before Christ. 
Many scientists believe that it was first grown by man in 
western Asia in the region of Mesopotamia. Barley and 
rice are of ancient origin ; but oats and rye seem to have 
been domesticated somewhat more recently. 

All the grains we have just mentioned were introduced 
into America by the early settlers. Corn (maize), however, 
is truly an American product, which was widely cultivated 
by the Indians both north and south of the equator, before 
Europeans came to this coast. Its origin also is a mystery,, 
for there is no single wild plant to which it can be traced. 
Corn was extensively cultivated by the ancient mound 
builders of North America, the cave dwellers and cliff 
dwellers of the Southwest, by the aboriginal inhabitants of 
Mexico, and by the subjects of the Incas of Peru to whom it 
furnished a food and in whose graves it is found in abundance.. 

Pod-bearing plants. Beans (111. p. 16), peas (111. p. 222), 
and their relatives are likewise especially important sources 
of food to man because they contain more protein, or nitrog- 
enous food, than any other group of plants. Hence they 
are a fair substitute in our diet for the more expensive meats. 
Another important plant belonging to this group is the 



FLOWERING PLANTS AND HUMAN WELFARE 299 



peanut. Its so-called nuts are really pods, which are de- 
veloped, not in the air like beans and peas, but in the 
ground, from peculiar flowers which penetrate the soil. 

Compound 
leaf 



Flower* 
stalk 



Flowers 




A two-seeded fruit, 
one seed cut in 
halves to show 

the two cotyledons 




A singl 
flower 

Attachment of- 
'peanuts to stem 



/Ground 
level 



——^Peanuts 
(fruits ) 



A complete plant with 
flowers and fruits 



A peanut plant 

Compare the peanut leaves, flowers, and fruits with similar organs in the pea plant. 
(See illustration, p. 222.) 

Other vegetable foods that form an important part of 
our diet are the leaves of cabbage heads, lettuce, and spinach ; 
the leafstalks of celery and rhubarb ; the stems and buds of 



300 



PLANTS AND HUMAN WELFARE 



asparagus and the flower heads of cauliflower and artichokes ; 
the roots of beets, carrots (111. p. 293), parsnips, turnips, and 
sweet potatoes ; and the tubers, or swollen underground 
stems, of the white potato. In all these vegetables, the 
plants, under cultivation, have manufactured and stored 




Courtesy of U. S. Department of Agriculture 

Sugar cane 
Unlike the corn-plant, which it resembles, the sugar plant lives for 4-6 years. 

away important food substances and vitamins. These 
coarser vegetable foods are also important in our diet since 
they form the " roughage " which acts as a tonic to the 
alimentary canal by stimulating the contraction of the in- 
testinal muscles. 

The white potato originated in western South America. 
It is often confused by early writers with the sweet potato, 



FLOWERING PLANTS AND HUMAN WELFARE 301 

from which it is very distinct. Like corn, beans, squashes, 
and pumpkins, both the sweet and the white potato are 
products of the New World which we have received as an 
inheritance from the Indians. The white potato gets its 
name " Irish potato " from the fact that at an early date 
it became an important food in Ireland, where it found espe- 
cially favorable conditions of soil and climate. 




Photography by R. B. Hoyt. From R. I. Nesmith and Associates 

Maple sugar trees 

Notice the pail on the largest tree. The sweet sap is being collected by the man at 

the right and is being boiled down to maple syrup or sugar in the large kettle. 

Sugar cane and beets are our principal sources of sugar. 
The structure of the flowers of sugar cane (111. p. 300) 
shows that it belongs to the grass family. Its stalks, after 
they are cut, are crushed between heavy rollers, and the 
sweet sap which is pressed out is boiled until it thickens into 
sugar. From the crude brown sugar thus obtained, pure 
white sugar is produced by purification and crystallization. 
Beets as a source of sugar are especially important since, 



302 



PLANTS AND HUMAN WELFARE 



unlike sugar cane, they can be grown in temperate regions. 
The percentage of sugar in sugar beets has been greatly in- 
creased by careful breeding and selection since the plant 
was first cultivated. Both sugar cane and beets are Old 

World plants. In 



early America the 
principal sources of 
sugar were the sugar 
maple in the North 
(111. p. 301) and cer- 
tain of the century 
plants in the desert 
regions of the south- 
western part of what 
is now the United 
States and in Mexico. 
In tropical regions 
sugar was also ob- 
tained by boiling the 
sap of certain palms. 
Cultivated fruits. 
The list of cultivated 
fruits available for 
the use of man is a 
long one. If you 
make a list of these 
fruits familiar to 
you, you can see how true the statement is. Fruits and 
vegetables new to us are introduced yearly by the Federal 
Office of Foreign Seed and Plant Introduction, being obtained 
by agricultural explorers in many distant lands. 

Plants as sources of beverages. Coffee is derived from 
the seeds of small scarlet berries of a tree, or shrub, which 




Courtesy of SunMst Photo 

A grapefruit tree 

Grapefruits are said to have received their name be- 
cause they grow in clusters like grapes. 



FLOWERING PLANTS AND HUMAN WELFARE 303 

grows wild in Abyssinia in Africa. This tree is now widely 
cultivated in Java and other parts of the East Indies, in 
Central America, in Brazil, and in other tropical countries. 
Tea is an infusion of the leaves of a plant allied to the beauti- 
ful camellias of our hothouses. It has been cultivated by 
the Chinese from time immemorial and is now widely grown 



' 




M 


7 «< ■■■■:,' 


; 






i£ 


it^ft^K^i 










^ \ ** 


jlk 1^ /^yjB^BBaE 


t' ''S;'"' 


''%HHHBir > " 


I 

» . m 






■y 


Hf % 


IklSm ' .- * Jp^W' 






** jfil 




P"*^ : 



Courtesy of Los Angeles Chamber of Commerce 

A date palm 

in Japan, Ceylon, and other tropical and subtropical coun- 
tries. Its culture was undertaken in South Carolina with 
very successful results as far as the plant itself was concerned. 
But owing to the price of labor, the tea produced in that 
state could not compete with imported teas, and the project 
was given up. Thein (the'm), the substance to which tea 
owes its stimulating effects, has been found by chemists 
to be identical with caffein (kaf'e-m), the active stimulant 



304 PLANTS AND HUMAN WELFARE 

in coffee. From the seeds of the fruit of the cacao, a tree 
of the tropical forests of Mexico and Central America, we 
obtain cocoa and chocolate, which may be regarded as foods 
as well as stimulants. 

Plants as sources of flavoring substances. The follow- 
ing products are used for flavoring our foods and beverages : 
vanilla, derived from the fermented fruit of a climbing orchid 
of the tropical forests of eastern Mexico ; pepper, from the 
dried berries of the pepper vine ; red pepper, from the fruits 
of Capsicum ; cinnamon, the pulverized bark of a tree 
belonging to the laurel family; ginger, prepared from the 
underground stalks of the ginger plant ; turmeric (used foi 
making curry powder) from an allied plant ; cloves, the dried, 
unopened flowers of a tree belonging to the myrtle family oi 
the Old World ; allspice, from the dried berries of an allied 
tree of tropical America ; mustard, from the seeds of a plant 
related to the cabbage and turnip ; horse-radish, from the 
pungent root of another plant of the same family ; many 
garden herbs, such as thyme, sage, and mints of various kinds 
and aromatic seeds, like anise and caraway. 

Plants as sources of drugs. Quinine, the well-known 
remedy for malaria, is obtained from the bitter bark of a 
tree known to botanists as Cinchona (sin-ko'na), which 
grows in the forests of Peru. This medicine is now obtained 
almost exclusively from trees that have been successfully 
introduced into Java. The camphor tree furnishes camphor 
gum. The fragrant leaves of wintergreen yield a volatile 
oil much used for flavoring foods and for medicines. The 
fruits of certain poppies yield opium from which morphine 
is made. From Old World plants related to the tobacco are 
obtained atropine and belladonna, which are used as narcotics 
from the hemp plant is prepared another narcotic, the hashisl 
of India. The leaves of the Peruvian coca, which have beer 



FLOWERING PLANTS AND HUMAN WELFARE 305 

used from prehistoric times by the Indians of that country 
as a stimulant, supply cocaine, a most valuable drug which 
enables severe surgical operations to be performed without 
pain. Other narcotic plants are the species of Nicotiana, 
which yield tobacco. 

Uses of Plants for Clothing 

Cotton. Second only to the use made of plants for food 
by man is the importance of plants in furnishing materials for 




Courtesy of Bureau of Plant Industry, U. S. Department of Agriculture 

Cotton plants and cotton 

At left, blossoms and unripe fruits ; center, a mature cotton plant ; right, cotton fibers 

and seeds, and mature cotton boll. 

clothing. In order to be valuable in this way plants must 
ievelop tough fibers of some sort that can be spun into threads 
md woven into fabrics. Cotton is so valuable in this par- 
ticular that before the Civil War the statement " Cotton is 
King " was common in the South. The cotton fiber is the 
nost important fiber of the world. Cotton plants (111. above) 
ome from seeds, which in our country are planted each year, 
md ordinarily grow to a height of two to four feet. The 



306 PLANTS AND HUMAN WELFARE 

fruits of these plants consist of cotton bolls, each of whic] 
when ripe bursts open and thus liberates twenty to fift; 
seeds covered with long white fibers. These fibers ar 
spirally twisted and can readily be spun into threads. Th 
invention of the cotton gin by Eli Whitney in 1792 revolu 
tionized the cotton industry, since formerly the separation o 
the cotton from the seeds had to be done by hand. Fron 
the seeds cottonseed oil is obtained. This oil is used in cook 
ing and soap making and as an adulterant of other oils. 

There is no region of the world better fitted for cottoi 
growing than is the Cotton Belt of our southern Unite< 
States. From this region comes at present about 60 pe 
cent of all the cotton produced in the world. In recen 
years, however, this most valuable product has been seriousb 
menaced by the cotton-boll weevil (111. p. 518), a long-nose( 
beetle which crossed the Mexican border in 1892. Thi 
pest has steadily advanced until it has spread over most o 
the Cotton Belt and it is causing great damage each year 
Thus far no way has been found to eliminate the insect 
but its ravages are checked by the use of poisons. Thii 
loss bears heavily upon all of us, for it means a smaller croj 
and, therefore, higher prices for clothing. 

Cotton was unknown in ancient Egypt. Fibers of severa 
species of cotton, quite distinct from those of the 01( 
World, were spun and woven by the inhabitants of th 
warmer parts of America before the arrival of Columbus 
Bolls of cotton were presented to him by the natives of th 
first islands he visited, and cotton fabrics woven by ther 
won his admiration. In prehistoric graves on the coast c 
Peru looms, spindles, and cotton, both spun and unspur 
have been discovered, and beautiful fabrics of cotton use 
for enveloping the South American mummies have bee 
unearthed. 



FLOWERING PLANTS AND HUMAN WELFARE 307 

Flax. From this most useful plant linen fabrics are pro- 
duced. The fibers used for this purpose form a part of the 
stem. After the pods are ripened, the plants are pulled, 
and the seeds removed. 1 The stems are then soaked in 
water for a time. By the growth of bacteria (p. 344) the 
valuable fibers are retted (that is, rotted or softened) so that 
they can be separated from the rest of the stem. They 
can then be spun and woven into linen. The botanical 
name (genus name) of flax is Linum (li'mfan). This is the 
origin of our words linen and line {e.g. fishline). Flax has 
been grown so long and so widely that we do not even know 
the country where it was first cultivated. " Fine linen " 
is frequently mentioned in the Bible; the Egyptian mum- 
mies were wrapped in linen ; and flax has been found in 
ancient Chaldean tombs. 

Other fiber plants. Hemp and jute furnish very tough 
material used in making ropes. The coconut palm supplies 
fibrous materials for the manufacture of mats. Straw hats 
and Panama hats are woven from the stems of various 
plants allied to the palms and the grasses. Century plants 
yield excellent fiber, and cordage of fine quality is made 
from the Philippine abaca (a'ba-ka'), commonly known as 
Manila hemp. Next to Manila hemp in strength and dur- 
ability is sisal (se-saT) hemp from which some of our 
strongest cord and twine are made. 

The Uses of Forests and Forest Conservation 

Uses of forests for fuel, lumber, and other commercial 
purposes. In the earlier days of our country's history all 
the fuel for heating and for running locomotives and other 

1 From the seeds of this plant is obtained the linseed oil used in mixing paints. 
After the seeds are ground and the oil has been removed, the residue is found to be 
excellent food for domestic animals. 



308 PLANTS AND HUMAN WELFARE 

engines was supplied from the forests. About one hundred 
years ago coal began to be used as fuel in Pennsylvania, 
and one would suppose that since that time our forests 
would have been drawn upon less heavily for fuel. It is 
estimated, however, that the United States burns annually 
at the present time more than 60,000,000 cords of wood. 
While we are considering the uses of plants as fuel, we should 
remember that our enormous coal beds were formed from the 
great tree ferns (111. p. 287) and other plants that lived in 
bygone ages. Petroleum, too, from which gasoline and kero- 
sene are produced, is a product of plant or animal decompo- 
sition ; and so also is natural gas. Artificial gas is made 
from coal and oil and so is indirectly derived from plants. 

One has but to call to mind the enormous use of trees for 
building purposes, for furniture, for railroad ties, for tele- 
phone and telegraph poles, for shipbuilding, for boxes, for 
barrels, and for. paper manufacture to realize how indispen- 
sable are our forests. Wood is used for the manufacture of 
artificial silk, rayon, of which about 140,000,000 pounds is 
made in the United States in a year — almost double 
our imports of raw silk. Artificial silk or " silk fiber " is 
made from the cellulose extracted from various kinds of 
light-colored, nonresinous woods, such as spruce, aspen, 
basswood, and cottonwood. This industry has grown 
enormously in the last few years, largely because of the great 
increase in the production of silk hosiery and underwear, 
and knitted sweaters and scarfs. Artificial silk is similar to 
real silk in appearance but is less expensive. The tanning 
extracts which are used in the manufacture of leather are 
derived mostly from the bark or wood of trees. However, 
the tanning of certain kinds of leather is now accomplished 
in an increasing degree by chemicals (not derived from 
plants) instead of by " tanbark," as formerly. Rosin and 



FLOWERING PLANTS AND HUMAN WELFARE 309 

turpentine, used in making paper, soap, varnish, and a 
variety of other products, come from our southern pine 
forests. 

The value of forests in regulating the flow of streams 
and preventing erosion. We turn now from a consideration 
of our forests as a source of fuel, lumber, and raw material 




Photograph by U. S. Forest Service 

Erosion of slope, due to deforestation 
Western North Carolina. 



for manufactured products to a discussion of their effects 
on the flow of streams. It is the general belief among 
foresters and nearly all other persons who are familiar with 
the conditions in mountainous regions that forests are of 
great value in protecting the soil from erosion (111. above) 
and in regulating the flow of streams. Let us see on what 
these beliefs are founded. 



310 



PLANTS AND HUMAN WELFARE 



When the rain falls upon the tree tops, the water drips 
from leaf to leaf and finally reaches the ground. Here it 
trickles down through the floor of the forest (111. below), 




_. , ,, , Photograph by U. S. Forest Service 

Floor of the forest 
Note the layers of decaying leaves (humus) and, in the foreground, numerous 

rootlets. 

which is formed of thick layers of decaying leaves, inter- 
lacing roots, and earth particles. All these form a porous 
mass which absorbs and holds back the water like an 
enormous sponge. The water thus retarded in its flow has 



FLOWERING PLANTS AND HUMAN WELFARE 311 

time to penetrate the earth, and hence it slowly reaches the 
water courses of the region without carrying away great 
masses of the soil. The time required for the run-off is 
increased, owing to the fact that the waters are spread out 
over a great surface instead of running down in gullies. 
The more rapidly the water runs, the greater its cutting and 
transporting power. 1 

Suppose now that the trees are removed from the mountain 
sides. After a time the forest floor disintegrates ; therefore, 
when the rains come, there is no effective way of absorbing 
the water. Instead, it flows rapidly over the surface of the 
land from which the trees have been cut, carrying away the 
rich topsoil and cutting deep gullies in the hillsides (111. 
p. 309). The material thus carried away fills up the river 
beds and harbor mouths, and in many cases a heavy expense 
is entailed in its removal. If the rain is long continued, the 
streams are swollen into torrents which may bring destruc- 
tion and death as they flood the valleys along their courses. 
While the forest floor may do much in holding back the 
water, it has, of course, like a sponge, a limit to the amount 
of water it can absorb. When this limit has been reached, 
if the rains continue, the water will run off on the surface 
and flood the streams in spite of the forests. 

Dangers that threaten our forests. When the early 
settlers reached this country, they found vast areas of virgin 
forest. Their first work was to clear land in order to get 

1 The erosive or cutting power of a stream varies as the square of the velocity. 
Thus if the velocity of a stream were increased from two to ten miles an hour, its 
cutting power would be multiplied twenty-five times instead of five times, as one 
might expect. The transporting power of water varies as the sixth power of its 
velocity. So if the velocity of a stream is increased 10 times, its transporting power 

s increased 1,000,000 times. A current of two miles per hour will move fragments 
jf stone the size of a hen's egg, weighing about three ounces; while a torrent of 

wenty miles per hour will carry bowlders weighing nearly one hundred tons. — 

forest Service Bulletin, No. 91, p. 14. 



312 PLANTS AND HUMAN WELFARE 

open spaces for cultivation and for protection from attacks 
of the Indians. They cut down the trees ruthlessly, anc 
the wood which was not needed was left to decay or become 
the prey of forest fires. Such forest destruction has con- 
tinued even to our own day. Now men are beginning 
to see that, unless this slaughter of trees is stopped, oui 
timber supply will soon be gone. In fact, Government 




Photograph by U. S. Forest Service 

Forest destruction by fire 
At left, a forest fire ; at right, the consequent waste of valuable timber. 

experts tell us that if the forest areas that yet remain 
are not protected from fire and kept productive, we shall 
soon suffer a timber famine. We are using up our timber 
two and one half times as fast as it is being replaced by 
young growth. The original forests of the United States 
covered 822,000,000 acres ; they have now shrunk to fivt 
eighths of that area and less than 100,000,000 acres of old- 
growth timber remains ! It is estimated that 84,000,00( 
acres of former forest land have been so severely cut anc 
burned as to become almost an unproductive waste, whicl 



FLOWERING PLANTS AND HUMAN WELFARE 313 

is equivalent to the combined forests of Germany, Holland, 
Belgium, Denmark, Great Britain, France, Switzerland, 
Spain, and Portugal. 

The threatened destruction of our American forests by 
careless methods of lumbering means not only the wholesale 
cutting of large areas without leaving seed trees to provide 






Jul 






Lit 1 , *i34l/* 




Photograph by U. S. Forest Service 

Plantation of yellow pine, eleven years after planting, Lolo National Forest, 

Montana 
Years hence this will be valuable timber. 

or future forest growth, but also the leaving of these acres 
trewn with dry branches and tops to become the prey 
)f destructive forest fires (111. p. 312). The annual loss 
)f property from this cause is conservatively estimated 
it more than sixty million dollars. The dead tree trunks 
md branches also furnish breeding places for insects which 
irey upon healthy trees. Other destructive agencies include 
various fungous diseases, such as the chestnut blight, which 



314 



PLANTS AND HUMAN WELFARE 



has practically exterminated the chestnut tree over a large 
part of its natural range, and the blister rust which attacks 
the white pines. If we are to preserve the remnants of 
our once vast forest resources, public sentiment must be 

thoroughly aroused 
which will compel the 
passage and enforce- 
ment of better con- 
servation laws. 

Necessity for re- 
foresting and for 
forest protection. 
Surely enough has 
been said to show the 
necessity for forest 
protection. Fortu- 
nately laws have 
been passed that en- 
able the National 
and some of the State 
Governments to ac- 
quire large tracts of 
land for forestry 
purposes. In many 
states these forest 
areas will protect the 
sources of large 
There is 
great need of trained 
experts to go through the forests, mark the trees which 
are mature enough to be cut, and decide what methods of 
cutting should be followed to keep the land producing trees 
for all time. Again, large areas already devastated should 




Photograph by U. S. Forest Service 

Approved methods of lumbering 
Note the logs in the distance, and the piles of brush streams, 
ready for burning in the foreground. 



FLOWERING PLANTS AND HUMAN WELFARE 315 

be replanted with young forest trees (111. p. 313). This is 
now being done to a considerable extent. In many foreign 
countries the forests are so used that year after year they 
supply the requisite timber and still continue to do their 
much-needed work in 
conserving soil and 
water. Such must 
be the policy in our 
country if we wish 
to escape most dis- 
astrous penalties 
that always result 
from forest destruc- 
tion. 

Organized protec- 
tion against fire is 
as essential in our 
forests as organized 
fire departments are 
in our cities. Sys- 
tems of lookout tow- 
ers (See 111.) from 
which fires can be 
detected quickly, 
telephone lines af- 
fording ready com- 
munication through- 
out the forest areas, 

roads and trails over which men and equipment can 
speedily reach fires, tools and machinery suitable for fight- 
ng hre, and men trained in the best methods of fre- 
ighting are necessary factors in efficient protection of 
orests. In recent years the airplane has come to be useful 




Photograph by U. S. Forest Service 

Latest type of fire lookout observatory, Cceur 
d'Alene National Forest, Idaho 
A man is stationed from daylight to dark during 
dangerous fire months of the year watching for signs 
of the smoke from forest fires. 



316 



PLANTS AND HUMAN WELFARE 



for patrolling forest areas and also for carrying fire-fighter! 
and supplies to remote districts that cannot be reachec 
quickly in any other way (111. below). 



Jn4 




Photograph by U. S. Forest Serci 



Forest patrol by airplane, Klamath National Forest, California 
In what respect is this method of forest protection superior to that shown on page 315 



Plants That Are Injurious to Man 

Weeds. Among the plants weeds are rightly regarde< 
by man as injurious. Any plant growing in cultivate 
ground to the injury of the desired vegetation, or to th 
disfigurement of the place, is considered a weed. Some c 
the characteristics of plants of this kind which make thei 



FLOWERING PLANTS AND HUMAN WELFARE 317 

difficult to contend with are these : (a) They can usually 
resist extremes of temperature ; (b) they can endure drought ; 
(c) they can grow in poorer soil and in more crowded con- 
ditions than can cultivated crops ; (d) they are usually not 
sought for food by insects or grazing animals, and they are 
resistant to plant diseases ; and (e) they produce enormous 
numbers of seeds which often, as in milkweed, cocklebur, 
and thistle, have most efficient 
provisions for seed dispersal. 

The introduction into our coun- 
try of many of these weeds is 
due to the fact that seeds of 
these plants were imported from 
Europe mixed with the seeds of 
grains. Finding, as did the Eng- 
lish sparrow and the gypsy moth, 
unusually favorable conditions 
for propagation here, these im- 
migrants have often spread over 
large areas and have brought 
great damage to cultivated crops. 
Among the worst of our weed 
enemies we may name black 
mustard, tumbleweed, pigweed, 
ragweed, and certain types of 
grasses. To keep them in check 
the farmer must cultivate and 
hoe his crops frequently. In a 
way, however, this is advantageous to the plants, since it 
keeps the soil stirred up and thus insures a better supply of 
air and moisture about the roots. 

Poison ivy (111. above) is a plant that should be familiar to 
everyone since ivy poisoning, though seldom fatal, is per- 




Poison ivy 
What are the distinguishing charac- 
teristics of this plant ? 



318 PLANTS AND HUMAN WELFARE 

haps one of the most uncomfortable experiences of the 
dweller in the country or of the visitor from the city. When 
one sees a woody vine trailing over the ground or clinging 
to trees by rootlets, bearing compound leaves having three 
leaflets, and in the autumn often with white berries, how- 
ever attractive the coloring of the leaves may be — beware! 
To touch this plant, or even to come near it, means for some 
people a distressing irritation of the skin and the formatior 
of blisters. The poisonous effect of this plant is due to i 
volatile oil formed in the leaves and stems. An effective 
treatment for ivy poisoning is an application of salt or a sugar- 
of-lead solution to the irritated parts or a thorough washing 
of the poisoned surface with suds made of yellow soap. 

Substances injurious to man produced from plants 
Opium, of which morphine is an ingredient, is obtained fron 
a thick, milky juice that comes from the fruits of the opiun 
poppy, and laudanum is made by dissolving opium in alcohol 
These substances are used in medicine to relieve pain. Un 
fortunately, opium is widely used, especially among Easten 
nations, for smoking. It is universally agreed that opiun 
smoking and the injection of morphine beneath the skii 
are demoralizing, degrading, and pernicious habits, and tha 
victims of the habits are sufferers both in body and in mind 

The Classification of Seed-Producing Plants 
Gymnosperms and Angiosperms. Seed-producing plant 
are still further subdivided into two groups. The first grou] 
includes all plants like the pines, hemlocks, and spruces, 1 
which the seeds are produced not in ovaries, but at the base o 
scalelike leaves, which are usually grouped together to fori] 
cones (111. p. 319) ; hence the name cone-bearing plants, whicl 
will apply to the common forms. The whole group is known a 
Gymnosperms ( j mi'no-spurmz, from Greek, meaning naked seeds] 



FLOWERING PLANTS AND HUMAN WELFARE 319 



Plants like beans, cucumbers, and oak trees, on the other 
hand, develop their seeds in ovaries, and these and all other 
plants of this type constitute 
the second of the two subdi- 
visions, which is known as the 
Angiosperms (an'ji-6-spurmz, 
from Greek, meaning having a 
vessel for seeds). 

Monocotyledons and Di- 
cotyledons. Again, the seed- 
producing plants may be clas- 
sified according to the number 
of cotyledons found in the 
seed. The corn (111. p. 231), 
gladiolus, and lilies, for ex- 
ample, have seeds with one 
cotyledon, and hence these are 
known as Monocotyledons (111. 
p. 320). Beans, peas, and maples, on the other hand, have 
two cotyledons and are therefore called Dicotyledons (111. 
p. 321). There are other striking characteristics which dis- 
tinguish these two groups of Angiosperms, as the following 
table will show : 




Mature cone 

From Gagefs "Fundamentals of Botany" 

Scotch pine 

Why is it that squirrels often distribute 

the seeds of this tree ? 



Number of cotyledons 
Veining of leaves . . . 
Stem structure .... 

Number of stamens and 
other parts of flower 



Monocotyledons 
(Corn, tulip, gladiolus) 



one 

parallel 

woody bundles scattered 

through pith 
based on plan of three 

or some multiple of 

three 



Dicotyledons 

(Bean, horse-chestnut, 

pansy) 



two 

netted 

bark, wood in distinct an- 
nual rings, pith in center 

based on plan of five or 
some number other 
than three 



320 



PLANTS AND HUMAN WELFARE 



Plant families. Continuing our classification of the angio- 
sperm group still further, we find that they are subdivided 



Diagram of cross 
section of a flower 
(the parts in 3's) 





Flower 



Section of a seed 
having an embryo 
with one cotyledon 



Woody' 
bundles 




-Rind 



Leaf, parallel-veined 



Stem with woody bundles 
scattered through the pith 

Rearranged from Gager's "Fundamentals of Botany' 

A monocotyledonous plant 



into more than 100 families, some of which are the lily 
family, the buttercup family, the rose family, and the pea 
family. This grouping into families is based largely upon 



FLOWERING PLANTS AND HUMAN WELFARE 321 



flower structure, and so it sometimes happens that an herb 
a,nd a tree belong to the same family. For example, the 
pea, bean, and the locust tree all belong to the pea family, 



Diagram of cross 
section of a flower 
(the parts in 5's) 





Section of a seed having 
an embryo with 
two cotyledons 




~Leaf, net-veined 



Stem with wood arranged 
in annual rings 

Rearranged from Gager's "Fundamentals of Botany' 

A dicotyledonous plant 



since they all have flowers and fruits closely resembling the 
pea flower. 

Plant genus. Again, each of the more than 100 families is 
made up of a varying number of more closely related plant 
groups, each of which is known as a genus (je'n^s, plural 



322 PLANTS AND HUMAN WELFARE 

genera, jen'er-a). The rose family, for example, has 24 or 
more genera, among which are the pear genus, the rose genus, 
and the plum genus. 

Plant species. Once more, each genus consists of a 
number of species, the members of which resemble each 
other very closely. The pear genus comprises the various 
" special kinds " (species) of pears and the apple genus the 
species of apples. Species, again, may be still further sub- 
divided into varieties, in which the plants are more closely 
related (for example, Baldwin, Greening, and Ben Davis 
varieties among apples). And finally a species (or variety) 
is made up of individual plants, that resemble one another 
in all essential respects. 

QUESTIONS AND APPLICATIONS 

1. From what two general points of view may plants be considered? 

2. Name the cereal plants and state the various ways in which they 
are useful. 

3. Tell what you can of the early history of wheat. 

4. Give the history of the use of the corn plant in America. 

5. Name the pod-bearing plants and show in what ways each is 
useful. 

6. Enumerate plants the following parts of which are useful to man 
for food : roots ; stems ; leaves ; flowers ; fruits ; seeds. 

7. Of what country is the white potato a native? Why is it called 
" Irish" ? 

8. What are the sources of sugar? How is sugar prepared? 

9. Name a number of fruits. Why are fruits especially useful in 
diet? 

10. What plants are sources of beverages? Describe each of these 
plants. 

11. Name some flavoring materials and the parts of the plant from 
which each is obtained. 

12. Give the sources of several common drugs. 

13. Tell the story of cotton. Name the enemies of the cotton 
plant. 



FLOWERLESS PLANTS AND HUMAN WELFARE 323 

14. State the sources of linen and describe the preparation of the fibers 
of which it is made. 

15. Name other fiber plants and give the use of each. 

16. Give an account of the uses of forests for fuel and timber. 

17. Show why it is believed that forests help regulate the flow of streams 
and prevent floods and erosion of soil. 

18. What are some of the dangers that threaten forests? 

19. Why are reforesting and the protection of forests necessary? 

20. Describe some of the means by which forests are protected. 

21. Name plants that are injurious to man and state in what way each 
is injurious. 

22. Name products, obtained from plants, that are injurious to man 
and state how each is injurious. 

23. Enumerate several ways in which the Federal Government has 
improved or protected the crops in our country. 

24. Discuss the topic : Is it justifiable for the United States Govern- 
ment to spend the people's money for agricultural investigations? 

25. What departments in your state government are responsible for 
the protection of forests or crops ? 

26. How are gymnosperms distinguished from angiosperms? Give 
examples of each. 

27. Name some monocotyledons and some dicotyledons you have seen 
growing. 

28. Complete this sentence by supplying the proper words in place of 
the letters : The Baldwin apple is a variety of the apple (a) which is a 
subdivision of the rose (b) which is one of the 119 (c) of the (d). 

PROBLEM 3. HOW ARE FLOWERLESS PLANTS RELATED 
TO HUMAN WELFARE? 

Pteridophytes (Ferns) 

The fern plant. We turn now from a discussion of seed- 
bearing plants to a consideration of those plants which never 
produce flowers or seeds. As a representative of the highest 
group of plants without seeds, we shall study the ferns 
(111. p. 324). The majority of ferns grow in damp, shady 
places. Among the common kinds we may name the brake, 



324 



PLANTS AND HUMAN WELFARE 



the maiden-hair, the rock fern, and the Boston fern, which 
is frequently cultivated in flowerpots. In any one of these 
ferns the leaflike parts above ground are known as fronds. 
The main axis of each frond runs throughout the leaf. In 
the case of compound leaves the leaflets are attached to 

each side. The leaflets may 








■ ■■■■'■ 




or may not be still further 
subdivided. Hence, a fern 
leaf is usually compound, 
and is strikingly graceful in 
its appearance. 

Beneath the ground the 
fronds grow from a stem 
called the rhizome (ri'zom), 
which is more or less en- 
larged for food storage, de- 
pending on the kind of fern. 
To this rhizome are attached 
the roots by which the plant 
is supplied with soil-water. 
The fern plant, therefore, 
like most seed-bearing 
plants, has all three kinds 
of nutritive organs (roots, 
stem, and leaves), and carries 
on carbohydrate manufac- 
ture in the green fronds, storing away the food in the rhizome, 
since the leaves die to the ground each year. The following 
spring the tiny leaves push up through the ground from the 
underground stem, unrolling and spreading their leaflets 
from the base to the tip. 

Fern spores. On the under surface of some of the leaflets 
of the ferns named above are little structures which are 



Courtesy of Brooklyn Botanic Garden 

Clayton's fern 
The fern leaves are known as fronds. 



FLOWERLESS PLANTS AND HUMAN WELFARE 325 



brown when fully developed. These are known as fruit-dots 
(sort, so'rl). Each fruit-dot, if examined with a microscope, 
is found to consist of several smaller objects known as spore- 
cases (111. p. 326). When these tiny spore-cases are ripe, 
they usually open gradually and then snap together with 
force, thus ejecting a powder, each particle of which is called 
a spore. Each spore con- 
sists of a single cell, which 
has a thick wall (111. p. 326). 

Fern prothallus. When 
the spores fall upon the 
ground and conditions are 
favorable, the single cell 
divides to form two cells 
(111. p. 326). By repeated 
cell division and by cell dif- 
ferentiation there is formed 
a tiny heart-shaped plant 
known as a prothallus (pro- 
thai 't£s) (111. p. 327), which 
has no resemblance to the 
parent fern that produced 
the spores. This tiny pro- 
thallus is held tightly to 
the surface on which it 
grows and is supplied with 
water and mineral matter by means of tiny outgrowths 
(rhizoids, ri'zoids), somewhat like root-hairs. Since the 
prothallus has chlorophyll, it can manufacture its own 
carbohydrates. 

On the under surface of each prothallus, in the region of 
the rhizoids, are minute organs, circular in appearance, 
known as antheridia (an^her-id'id, sperm-producing 




Courtesy of Brooklyn Botanic Garden 

Underside of a fern leaf 

Observe the numerous bodies, " fruit 
dots " (sori) in which sporangia are found, 
from which spores come. 



326 



PLANTS AND HUMAN WELFARE 




From Gager's " Fundamentals of Botany " 

Section of a fern leaf 
A spore case (sporangium) contains a large 
number of spores. The spore case below has 
opened and expelled a number of spores. 



organs), in which are produced a large number of sperm cells 
(111. p. 328) . Each sperm cell has many threadlike swimming 

organs. At a little dis- 
tance from the antheridia, 
near the notch in the pro- 
thallus, are found some- 
what flask-shaped bodies 
called archegonia (ar'ke- 
go'ni-a, egg-producing or- 
gans). In each of these 
there is developed a special 
cell known as the egg cell 
(111. p. 328). 

Fertilization and devel- 
opment of the egg cell. 
When the sperm cells are 
ripe, they escape from the sperm-producing organs. They 
swim through the thin film of moisture on the under side of 
the prothallus until 
they come to the 
opening in the egg- 
bearing organ (111. 
p. 328). Finally a 
single sperm cell 
reaches and enters 
the egg cell. When 
the nucleus of the 
sperm cell has com- 
bined with the nu- 
cleus of the egg cell, 

fertilization is com- 
, , Development of a fern spore into a prothallus 

piet . A, section of a spore; B, first cell division of a spore; 

The fertilized egg C, D, later stages in the formation of a prothallus. 




FLOWERLESS PLANTS AND HUMAN WELFARE 327 



cell (111. p. 328) now divides, as in the egg cell of the fish, 
and thus a two-celled stage is reached. Cell division con- 
tinues, just as in the fish. The cells change in their struc- 
ture and functions (cell differentiation) and thus form the 
organs of a spore-bear- 
ing plant, like that de- 
scribed on page 324. 

Alternation of gen- 
erations. Thus we see 
that in the life-history 
of the fern plant we 
have two distinct gen- 
erations. The first is 
the ordinary fern 
plant, which is familiar 
to all, and which is 
known as the asexual 

generation Or Spore gen- After Margaret C. Ferguson 

eration y because the Fern prothallus 

spores formed on the ..^^ZSKtS 

fronds produce the next producing organs (antheridia) below them near the 

generation (prothallus) rootUke structures - 

without fertilization or the union of two kinds of sex cells. 
The second generation, the prothallus, is the sexual genera- 
tion, because, as we have seen, it can produce a fern plant 
only from the fertilized egg cell. In plants like the fern, in 
which an individual (fern) produces another plant (prothal- 
lus) unlike itself, and this in turn gives rise to a plant like the 
original (fern), we have so-called alternation of generations. 

Bryophytes (Mosses) 

The moss plant. A second group of flowerless plants 
includes the mosses. In general, mosses are smaller plants 



^^^8V^n? lip .%$!§£ 


-C\y3~P<SS9M 


v -^ /^^SfnSL «^ 



328 



PLANTS AND HUMAN WELFARE 



Egg ce// 



than the ferns, but like them are usually found in damp, 
shady places. If one examines a moss plant when it is " in 
fruit," a slender stem will be seen projecting from the leafy 
part below. At the upper end of this slender stem, a cov- 
ered cuplike structure is evident (111. p. 329). This cup, or 
capsule, as it is called, is filled with tiny dustlike particles, 

which when examined with 
a compound microscope 
prove to be cells. They 
are the spores (111. p. 330). 
The spores are reproductive 
bodies similar to those pro- 
duced in the spore cases of 
ferns. 

The moss protonema. 
When these bodies are ripe, 
the capsule opens and dis- 
charges some of the spores, 
which fall to the ground 
and soon begin to grow, 
forming at first an elon- 
gated cell (111. p. 330), 
which later divides, giving 
rise to two cells. This 
process continues until a 
slender, green, threadlike 
mass is formed, with many branches. This threadlike mass 
is called the protonema (pro'to-ne'md, " first thread") (111. 
p. 330). Some of the branches produce buds which finally 
grow into the leafy structure which we know as the moss 
plant (111. p. 329). 

The sexual generation of the moss. At the top of some 
moss plants at certain seasons of the year, in the midst of the 




<a -'4 
Sperm cef/s^H. 

Redrawn from Gager's "Fundamentals of Botany" 

Egg-producing organ (archegonium) of a 
fern prothallus (highly magnified) 

Sperm cells are entering the tube of the 
archegonium on their way to the egg cell. 






ELOWERLESS PLANTS AND HUMAN WELFARE 329 



,-— - Spore ■ 
case 



Rhizoids 




rosette of green moss leaves, may be found tiny flask-shaped 
organs, the archegonia (111. p. 330). At the base of each of 
these organs is produced an egg cell. 
Sometimes in the same moss plant, and 
sometimes in another, are to be found 
club-shaped organs called antheridia 
(111. p. 330). In the antheridia are 
produced sperm cells. At the proper 
time the sperm cells make their way 
into the archegonia, and when a sperm 
cell reaches an egg cell, they fuse, the 
two nuclei unite, and a fertilized egg 
cell is formed. This fertilized egg cell, 
by the process of growth and cell divi- 
sion, finally forms the slender stalk with 
the capsule containing spores at the 
end of it (111. at right). 

Alternation of generations in the 
moss. The protonema and the leafy 
shoots with their antheridia and arche- 
gonia are known as the sexual genera- 
tion because it is this plant that pro- 
duces eggs and sperm-cells which must 
unite before the egg can develop into 
the spore-bearing plant. The slender 
stalk with the capsule at the end which 
is produced by the fertilized egg cell is 
called the asexual generation, since the 
spore-bearing plant can reproduce with- 
out the union of two kinds of cells. The spore-bearing plant 
is dependent on the leafy plant for all its food. In the fern, 
on the other hand, it is evident that the spore-bearing plant 
and the plant producing eggs and sperms are entirely inde- 



plant Young 
with moss plant 
spore case 




Enlarged view 
of spore case 

A moss plant 

Why is the part of the 
moss plant above the 
" leaves " called the asex- 
ual generation ? 






330 



PLANTS AND HUMAN WELFARE 




Spore 
germinating 

to form 
protonema 



Branching 
protonema 



The moss protonema 

How does a moss spore form the 
sexual generation ? 



pendent plants. In both of these 
groups of seedless plants, how- 
ever, there is an alternation of 
generations. 



Thallophytes 

Algce 

Spirogyra. Anyone who has 
ever been in parts of the country 
where ponds or very slowly mov- 
ing bodies of water abound must 
have noticed either at the bottom 
or on the surface of the water a green, slimy mass. It is so 
frequently found on the surface that it is called " pond 
scum." If one examines a small portion of this mass even 
with the naked eye, one will see 
that it consists of a great num- 
ber of interlacing threads. When 
looked at with the compound 
microscope, each of these threads 
is seen to be a series of cells joined 
end to end. All the cells are prac- 
tically the same in shape and struc- 
ture, however, so that a study of 
one will make clear the structure 
of all. 

Inclosing each cell there is a thin 
cell wall. The first structures one 
is likely to notice within the cell 
are the chlorophyll bodies. In the 
pond scum, known as Spirogyra 
(spi'ro-ji'rd), the chlorophyll is ar- 




Sperm-produc 
\ ing organ 
with escaping 
\ sperm cells 



Section of 

egg-producing 

organ 



Reproductive organs of a moss 
plant 

Why are these bodies called sex- 
ual organs ? 



FLOWERLESS PLANTS AND HUMAN WELFARE 331 



\Chlorophyll 
bands 



--Nucleus 

''Protoplasmic 
membrane 



•Cell wall 



ranged in spiral bands, and it is this which has given the 
plant its name (111. below). In other forms the chloro- 
phyll is differently arranged, sometimes in star-shaped 
masses, one in each half of the cell, and sometimes diffused 
throughout the cell. If a little iodine is added to the speci- 
men when it is being examined under the microscope, a 
nucleus may be distinguished near the center of each cell 
(111. below, right). In the cytoplasm and nucleus the pro- 
toplasm appears as 
a clear and almost 
transparent mass. 

The thread or fila- 
ment continues to 
increase in length by 
the growth and divi- 
sion of certain indi- 
vidual cells that 
compose it. At the 
close of the season 
most of the filaments 
perish, but some of 
them undergo pecu- 
liar changes. The 
bands of chlorophyll lose their definiteness, the protoplasm 
becomes massed, tiny outgrowths from the sides of the cells 
occur, and these continue to extend till they meet simi- 
lar outgrowths from a neighboring filament (111. above, left). 
These outgrowths unite, and thus a tube from one cell to 
the other is formed. The contents of one cell pass through 
to another, and the two masses fuse. A thick wall forms 
about the united mass and the old cell walls decay and fall 
away, leaving these thick-walled zygospores (zi'go-sporz) 
on the bottom of the pond. In the spring the protoplasm 



Zygospores ''l 



Contents of- 
two cells 
fusing 

Contents of one- 

cell entering 

the other 

Bands of — 
chlorophyll 
breaking up 




Conjugation of 
two filaments 



Single cell 
of filament 



Spirogyra 
How does this plant differ from a bean plant in 
structure ? In what respects are these plants alike in 
function ? 



332 PLANTS AND HUMAN WELFARE 

within each of these zygospores begins to grow, breaks 
through the thick wall, and proceeds to form a new filament 
by cell division. The formation of the zygospores is known 
as conjugation; it is a kind of sexual reproduction, though 
the two cells taking part in the process are the same in 
appearance. 

If one observes pond scum on a sunny day, bubbles will 
be seen escaping from the mass. A test of this gas proves 
it to be oxygen, and as we should expect, it occurs in 
connection with the process of carbohydrate manufacture 
just as in other green plants. In fact it has been proved 
that these simple plants manufacture foods, digest, assimi- 
late, respire, and reproduce as do the higher plants we have 
studied. The differences, then, between a simple plant like 
Spirogyra and a bean plant or an oak tree are mainly those 
of structure and adaptations for the performance of func- 
tions which are largely common to both. Indeed, it is evi- 
dent that every cell of the Spirogyra is in contact with the 
water, from which all the substances needed are obtained by 
absorption. Hence, any special adaptations for securing 
food materials or of giving off wastes, such as are found in 
higher plants, are unnecessary. 

Spirogyra and Pleurococcus (111. p. 221) are only two of a 
large number of simple plants known as algce (al'je). They 
differ widely in form, but none of them develop roots, stems, 
or leaves. Among the most common algae are the marine 
forms known as seaweeds, of which there are many kinds. 

Fungi 

YEAST 

Microscopical appearance and size of yeast. A small 
piece of a cake of compressed yeast, mixed in a spoonful of 



FLOWERLESS PLANTS AND HUMAN WELFARE 333 



water, forms a milky fluid that is much like so-called bakers' 
or brewers' yeast. If we examine with the microscope a bit 
of this mixture in the same way in which Pleurococcus was 
studied, we find that it consists of innumerable bodies of 
minute size. These are yeast plants (111. below). Each plant 
is unicellular, more or less egg-shaped, and composed of 
colorless protoplasm inclosed within a wall of cellulose. By 
the use of special stains, a nucleus becomes visible. The 
spherical dots seen in fresh yeast cells are known as vacuoles 




Vacuole 





—Bud 




■1 Nuclei 
/ 

^Cytoplasm 
-Cell wall 



Nucleus 



Cell 
budding 



Division 
completed 



A yeast plant 
Describe the changes that are shown in this illustration. 

(vak'u-olz) and are filled with a colorless liquid. Yeast is 
regarded as one of the lowest forms of plant life. 

Reproduction of yeast. Most of the cells that we are 
looking at are not separate individuals, but are strung to- 
gether in little chains. This fact leads us to a discussion of 
the method of reproduction of yeast. When there is a suffi- 
cient supply of food, moisture, and oxygen, and when the 
temperature is favorable, these living plant cells begin to 
feed and to grow. They soon reach their full size, and then 
the cell wall is pushed out at the side by the growing proto- 
plasm. In this way a bud is formed. This continues to 
grow and soon becomes a daughter cell, closed off from the 
mother cell by a wall of cellulose. Meanwhile, one or more 
buds may be forming on the outside of the daughter cells. 



334 PLANTS AND HUMAN WELFARE 

If all these cells cling together, a colony is formed which con- 
sists of a mother cell (largest in size), one or more daughter 
cells, and several tiny granddaughter cells. The individual 
cells are easily separated from one another. This method 
of reproduction is known as budding (111. p. 333). 

Changes caused by yeast. A yeast mixture may easily be 
prepared for experimentation by pouring into a jar a cup of 
water, adding a spoonful of molasses, and a spoonful of the 
milky fluid made as described on pages 332-333. 

If the jar with its contents is set aside in a warm place 
(70° to 90° F.) for a short time, it begins to " work," and 
bubbles of gas rise to the surface. At the end of several 
hours, we notice that the sweetness of the molasses is dis- 
appearing, that the mixture begins to smell sour, and that a 
sharp, biting taste is becoming evident. The sugar in the 
mixture can no longer be tasted because it has been de- 
composed into two compounds. One of these is the gas in the 
bubbles. This gas is carbon dioxid. The other substance 
is alcohol. Both these changes are caused by the action of 
the growing yeast plants upon the sugar in the molasses. 

Use of yeast. When bread is made, water (or milk), 
butter, salt, sugar, and yeast are added to flour. After the 
mixture has been stirred together, a sticky mass of dough 
is formed, which in a warm place begins to rise. This is due 
to the fact that the yeast cells change the sugar into alcohol 
and carbon dioxid. Bubbles of gas are thus imprisoned in 
the sticky dough. While expanding and seeking to escape, 
they make the solid mass porous. After the bread has risen 
sufficiently, it is kneaded in order to break up the large bub- 
bles and in order to distribute the gas throughout the dough. 
When the bread is baked, the alcohol and carbon dioxid pass 
off into the air, leaving the bread light and more easily 
digestible. 



FLOWERLESS PLANTS AND HUMAN WELFARE 335 



BREAD MOLD 

Structure of bread mold. If pieces of bread or cake be 
moistened and placed in a dish and covered with a bell- jar 
in the dark, in a few days grayish patches will appear in 

places on the surface 

Sporangia or_ 
spore casesZ 



of the food. This 
growth is due to the 
activity of one of the 
fungi, known as a mold, 
and will probably be 
the kind called bread 
mold. No care is re- 
quired to produce the 
plant in quantities ; on 
the contrary, as com- 
mon experience shows, 
some pains must be 
taken by the house- 
keeper to prevent it 
from spoiling food. 

When the bread mold 
is examined with a hand 
lens, it is seen to con- 
sist of a mass of fine 



Spores 




A mold plant 
Which parts are concerned with nutrition and 
which with reproduction ? Can this plant manu- 
facture food ? 



interlacing threads called the mycelium (mi-se'li-#m). (See 
111. above.) Single threads are known as hyphce (hi'fe). 

Reproduction and life history of bread mold. Some of 
the hyphae in their growth assume an upright position, and 
each of these at the upper end develops a little globular white 
mass or spore case. (See 111. above.) An examination with 
the high power of the microscope shows that the spore cases 
are filled with tiny cells known as spores. When the spores 



336 



PLANTS AND HUMAN WELFARE 






are ripe, the spore cases appear brown or black, they break 
open, and the spores are scattered. If these spores fall on 
food of some kind, such as bread, they begin to germinate, 
and each one produces another mass of threads with spore 
cases on erect hyphse. In other words, the mold produces 
spores and the spores reproduce the mold. The spores of 
molds are in the air nearly everywhere ; hence we see why 
molds appear so quickly on foods of various kinds, provided 

they are moist and in a 
warm place. 

Nutrition in the fungi. 
Molds, like other fungi, as 
we have already said, can- 
not manufacture their own 
food out of the materials 
obtained from the soil and 
air, but are dependent on 
foods made by green plants. 
Certain of the threads called 
the nutritive hyphce form fer- 
ments which digest the food 
compounds found in bread or other substances on which the 
mold is growing, and then the digested food is absorbed and 
used in growth and in the production of energy. Other 
threads develop the spore cases and so are called reproduc- 
tive hyphce. Hence, it is evident that fungi, like all plants, 
carry on both nutritive and reproductive functions, but on 
account of the lack of chlorophyll are, like animals, dependent 
on the green plants for their supply of food. 




A mushroom 

The spores are developed in the thin plates 

within the umbrella. 



OTHER FUNGI 



Mushrooms. 

which are often 



igi 



Mushrooms (111. above) are forms of fun 
called " toadstools," especially if they are 



FLOWERLESS PLANTS AND HUMAN WELFARE 337 



supposed to be poisonous. All fungi of this kind should, 
however, be called mushrooms, since their structure and life 
history are similar. The conspicuous part of the plant, the 
umbrella-shaped structure so familiar to all, is really the 
reproductive organ of the plant, namely, the part that bears 
the spores (111. p. 336). 
The nutritive organs are a 
mass of threads (as in the 
mold) which lie beneath the 
surface, where they absorb 
the foods from some decay- 
ing material in the soil to 
give rise to the reproduc- 
tive body. 

As indicated above, many 
mushrooms are poisonous, 
but a few kinds are known 
to be edible * (111. p. 336). 
Mushrooms are not espe- 
cially nutritious ; that is, 
they cannot take the place of 
the cereals and other staple 
foods, but they serve to add 
to the variety of materials 
which are more valuable for 
their flavoring qualities than 

for the quantity of nutriment they contain. Commercially 
the cultivated mushroom is of considerable importance, es- 
pecially in Europe. Paris is said to be the center for the sale 
of this product. In this country the mushroom is of com- 
mercial importance only in the regions of the larger cities. 




Corn smut 
Note that this fungus has destroyed the corn 



1 So many deaths are caused by using poisonous instead of edible mushrooms 
that it is never safe to eat wild forms until they have been identified by an expert. 



338 PLANTS AND HUMAN WELFARE 

Rusts and smuts. The fungi known as rusts receive their 
name from the rusty appearance in an early stage of their 
growth which they cause on the stems and leaves of plants 
which they attack. The cereals, wheat, oats, barley, and rye, 
are the crops which this fungus injures most. In the case 
of wheat, half of the crop or even more may be destroyed. 

The very descriptive name of smut is given to another fun- 
gus which affects all the cereals named above, and corn as 
well (111. p. 337). In the case of corn, this plant often affects 
the ears as well. The name is probably given on account 
of the appearance of the mass of black spores. If one 
touches these spores, especially those of corn smut, with the 
ringer, and then rubs the finger on some white paper or cloth, 
a sooty mark is left. The damage done by smuts is very 
considerable. In case of the corn crop alone it has been 
estimated that a yearly loss of 20 per cent of the crop, or 
$200,000,000, is caused thereby, and in the other cereal crops 
the loss is even greater. It should be mentioned in closing 
this discussion that the rusts and smuts are only two of a 
large number of fungous diseases that affect plants. 

On account of the importance of bacteria in relation to 
human welfare Problem 4 has been devoted to this group 
of fungi. 



QUESTIONS AND APPLICATIONS 



1. In what three respects are ferns like the seed-producing plants? 

2. Where are the fruit-dots found on fern plants, and what do they 
contain ? 

3. How are the spores of a fern scattered ? Why is dispersal of spores 
an advantage to the next generation ? 

4. Describe the formation of the prothallus. In what ways does the 
fully developed prothallus differ in structure from the fern plant ? 

5. Describe the structure, location, and function of each of the repro- 
ductive organs of a prothallus. 






BACTERIA AND HUMAN WELFARE 339 

6. Why is the prothallus called the sexual generation of the fern ? 

7. Describe the formation of a new fern plant. 

8. Compare the asexual generation of the moss and fern. 

9. Why is Spirogyra called pond scum? 

10. Why has Spirogyra no need of roots, stems, or leaves? 

11. Describe the formation of zygospores in Spirogyra. How are these 
bodies of advantage ? 

12. In what respect is Pleurococcus simpler in structure than Spirogyra ? 
(See p. 221.) 

13. If you were lost in the woods how might the location of Pleuro- 
coccus on the trunks of large trees help you to determine one of the points 
of the compass ? 

14. What parts present in seed plants and ferns are lacking in the algae ? 
How do alga? carry on nutrition ? 

15. Name five kinds of fungi, and state the economic importance of 
each. 

16. What is the principal difference between fungi and alga? in nutrition 
functions ? 

PROBLEM 4. HOW ARE BACTERIA RELATED TO HUMAN 

WELFARE ? 

Health and Disease 

What is meant by health. We have already considered 
the various activities that must be carried on by all living 
organisms if they are to continue their individual existence 
and perpetuate their kind. When these nutritive and re- 
productive functions are performed by the organs, tissues, 
and cells of the plant, animal, or man under favorable 
external and internal conditions, the organism is in a healthy 
condition. Too much emphasis cannot be laid upon the 
importance of maintaining health, for thus only can man 
attain happiness for himself and others and do his part in 
the world's work. The healthy organism is one in which all 
the cells are working together, or cooperating under favorable 
conditions, for the common good. 






340 PLANTS AND HUMAN WELFARE 

What is meant by disease. The cells of living things, 
however, are often unable to do their own work effectively 
or to cooperate with other cells to the fullest extent. As a 
result the whole organism may fail to develop normally, 
or it may even cease to function and die. This inability of 
cells to function properly may be due to a variety of causes. 
In man and higher animals these abnormal conditions often 
give rise to sensations of discomfort or pain. The person is 
ill at ease — hence the term disease (from the Latin dis, 
meaning absence of and ease). The term disease may refer 
either to such a mild disturbance as that caused by over- 
eating, or to the very serious symptoms that often occur in 
cases of typhoid fever or pneumonia. In its broadest appli- 
cation, therefore, the term disease may be used whenever the 
work of the cells of a living organism is being interfered with, 
even though there may be no evidence of pain or discomfort. 

Common ideas as to disease and its causes. The earliest 
records of human history show that man was a victim of dis- 
eases, probably much the same as those which attack him 
now. Various beliefs were held as to the cause of these 
bodily ills. Many of the earlier races regarded disease as 
due either to evil spirits or to punishment by the gods; 
hence medical treatment was closely associated with re- 
ligious rites and incantations. Among uncivilized peoples 
these ideas still prevail. Indeed, it is astonishing how 
ignorant and credulous the average individual is, even among 
the more enlightened peoples, in matters relating to the 
cause and treatment of sickness. For instance, various 
charms are sometimes worn to ward off disease, horse-chest- 
nuts are carried in the pocket to cure rheumatism, warts are 
believed to disappear as a result of magic, and certain herbs 
are supposed to owe their efficacy to the fact that they were 
gathered at definite phases of the moon. The enormous 






BACTERIA AND HUMAN WELFARE 341 



sale of patent medicines in our country has been due largely 
to the willingness of the average individual to believe in the 
claims of those who advertise the cures wrought by the use 
of these nostrums. 

What science has revealed regarding the causes of dis- 
eases. Medical science has proved that a large number of 
diseases which afflict humanity are due to various living 
organisms, most of them microscopic in size, which have 
found favorable conditions for growth within or upon another 
organism. There these organisms give rise to conditions that 
are recognized as diseases of various kinds. As examples of 
diseases thus caused we may mention tuberculosis, diph- 
theria, and typhoid fever, and the rusts and smuts that 
grow on wheat and corn. 

Discovery of the relation of microscopic organisms to dis- 
ease. On pages 20-23 we discussed briefly the use of the 
microscope in the discovery of the cells of which the higher 
plants and animals are composed. It was the Dutch investi- 
gator Leeuwenhoek (111. p. 18) who also found that water in 
which dead plant or animal material was decaying contained 
countless microscopic plants and animals. Some of the 
living forms were changing shape ; others were capable of 
rapid motion ; still others were tiny rod-shaped plant cells, 
now called bacteria. 

As early as the eighteenth century it was suggested that 
such microorganisms might be the inciting causes of certain 
diseases. About 1873 the germ theory of disease was estab- 
lished. To Pasteur (Frontispiece) we are deeply indebted 
for the application of this knowledge to the prevention and 
cure of infectious diseases in plants, animals, and man. 

But we must emphasize the fact that in reality only a 
relatively small number of kinds of microorganisms have 
any relation to disease. Indeed, the great majority are 






342 



PLANTS AND HUMAN WELFARE 



either harmless or distinctly beneficial. We are now to 
learn something of one great group of the microscopic plants 
already referred to as bacteria. 

Structure, Growth, and Reproduction of Bacteria 

Appearance and size of bacteria. Every one knows that, 
when a bouquet of flowers is left for some time in a vase of 
water, the stems decay and give off disagreeable odors. 
This is a common example of the action of bacteria, for 




Courtesy of Dr. William H. Pari: 

Different forms of bacteria (highly magnified) 
From left to right : spherical-shaped (cocci) , rod-shaped (bacilli) , spiral-shaped 

(spirilla) . 

decay is usually the result of the work of these organisms. 
When we examine the stems or the putrid water, we find 
a slimy scum. If we put a drop of this scum on a slide 
under a cover glass and examine it with the highest powers 
of the microscope, we usually see many different forms of 
living things. Some of them, the single-celled animals, 
appear relatively large. A closer examination under the 
high powers of the microscope will disclose in the water 
countless numbers of very minute organisms ; these are the 
bacteria, which have several characteristic shapes. Some 
are spherical (cocci, kok'si, singular, coccus, kok'tts), some 






BACTERIA AND HUMAN WELFARE 343 



are rod-shaped (bacilli, bd-sil'i, singular, bacillus, ba-siYus), 
and still others are spiral in form (spirilla, spi-ril'd, singular, 
spirillum, spi-ril'#m), (111. p. 342). Each bacterium is a 
translucent bit of protoplasm with no definite nucleus. Be- 
cause of their structure and method of nutrition biologists 
now regard them as plants rather than as animals. 

Some kinds of bacteria have one or more long hairlike 
projections from the ends (flagella, fld-jel'd, singular flagel- 
lum) which lash about rapidly and thus drive the individual 
through the water (111. p. 366). Spiral bacteria roll over and 
over and advance like a corkscrew. 

It is very difficult to get any conception of the extreme 
minuteness of bacteria ; indeed, bacteria vary in size from 
those that can be seen when enlarged 100 times to those 
that are so tiny that they scarcely can be distinguished 
when magnified 1000 times. The imagination may be some- 
what assisted if we remember that 1500 rod-shaped bacteria, 
arranged end to end, would scarcely reach across the head 
of a pin. 

EXERCISE 58 

Microscopic study of bacteria. Laboratory demonstration. 

Put some chopped hay in a bottle of water, and allow it to stand 
in a warm place for several weeks, until decay has set in and a scum 
has formed over the top of the water. Place on a glass slide a drop 
of this scum, and cover it with a cover glass. Examine with the 
highest power of the compound microscope. 

1. Describe the source of the material you are examining. 

2. Which of the different forms of bacteria shown on page 342 do 
you find? Draw several of the different shapes that you see, highly 
magnified. 

3. Do any of the bacteria seem to be in motion? If so, describe the 
motion. 

4. Add a drop of eosin or red ink or iodine to one side of the cover 
glass and then examine the bacteria. State the result. 



344 



PLANTS AND HUMAN WELFARE 




Courtesy of Dr. William H. Park 

Petri dishes with nutrient agar 
Dish at left with few colonies (each produced by a 
single bacterium) ; dish at right with many colonies. 



Reproduction of bacteria. When conditions are favorable, 
the production of new bacteria goes on with marvelous rapid- 
ity. The process is 
somewhat as follows : 
The tiny cells take 
in through the cell 
wall some of the food 
materials that are 
about them, change 
this food into proto- 
plasm, and increase 
somewhat in size. 
The limit is soon 
reached, however, 
and the bacterium 
begins to divide crosswise into halves, as does Pleurococcus. 
The mother cell thus forms two daughter cells asexually by 
making a cross partition between the two parts. If the 
daughter cells cling together, a chain (111. p. 345), or a mass, 
is formed. Often they separate 
entirely from each other. In either 
case the whole mass of bacteria is 
called a colony (111. above). 

It usually takes about an hour 
for the division to take place. 
Suppose that we start at ten o'clock 
some morning with a single healthy 
bacterium. If conditions were fa- 
vorable, there would be two cells at 
eleven o'clock ; by twelve each of 
these two daughter cells would have 
formed into two granddaughter cells ; the colony would then 
number four individuals. Figure it out for yourself, and 



1st hr. 2nd hr. 3rd hr. 

hthhr. 

1th hr. 



6th hr. 

Reproduction of bacteria 
through the sixth hour 

How many bacteria would be 
shown in the diagram if it were 
completed through the twelfth 
hour? 






BACTERIA AND HUMAN WELFARE 345 



you will see that if this process should continue unchecked 
for twenty-four hours, the colony would number 16,777,216 
bacteria. Such startling possibilities as those just suggested, 
fortunately, seldom become realities, for some of the favor- 
able conditions soon cease to exist and the bacteria either 
die or cease to multiply. 

Spores formed by bacteria. Sometimes, when food or 
moisture begins to fail, the protoplasm within each cell 
rolls itself into a ball and covers itself with a much thickened 




Courtesy of Dr. William H. Park 

Spore-forming bacteria 
In what part of the bacteria at the left of the picture are spores formed ? Where 
are the spores formed in the bacteria in the central picture ? What is the arrangement 
of bacteria and spores in the picture at the right ? 

wall. This protects it until it again meets with conditions 
favorable for growth. This process is known as spore 
formation; the tiny protoplasmic sphere, with its dense 
covering, spore wall, is called a spore (111. above). In this 
condition bacteria may be blown about as a part of the dust. 
They may be heated even above the temperature of boiling 
water without being killed. When at length they settle 
down on a moist surface that will supply them with food, 
the spores absorb moisture, burst their thick envelope, 
assume once more their rod-shaped or spiral form, and go 
on feeding, assimilating, and reproducing their kind. 



346 PLANTS AND HUMAN WELFARE 

Growth of bacteria. Like other plants and animals bac- 
teria must have food, moisture, some source of oxygen, 
and favorable temperature. These necessary conditions 
are secured in culture dishes prepared as follows : A Petri 
dish is first cleaned and then heated hot enough to kill any 
living organisms that may be in it. Then it is partly rilled 
with a hot jellylike solution which contains the food sub- 
stances bacteria need. On cooling, this food substance 
forms into a solid layer on the bottom of the dish. Thus we 
supply all the essential conditions for the culture of bacteria, 
and all that is necessary is to bring the germs in contact with 
the sticky surface. Bacteria may also be cultivated in 
test tubes that have been sterilized by heat and then partly 
filled with sterile beef tea, gelatin mixture, or potato, the 
tubes then being plugged with cotton. 

Note to the Teacher. Preparation of culture dishes for raising 
bacteria. To prepare 1000 cc. (about a quart) of agar mixture, weigh out 
10 grams of salt, 10 grams of peptone, 10 grams of Liebig's beef extract, 
and 10 grams of agar. Measure into an agate stewpan 1000 cc. of water, 
and stir in the salt, peptone, beef extract, and agar (the latter having been 
cut into small pieces) . Heat the mixture in a double boiler until the agar 
is wholly melted. Slowly stir in just enough baking soda to cause red 
litmus paper to turn blue (i.e. the mixture should be slightly alkaline). 
When the pieces of solid agar have all disappeared, the hot liquid should 
be filtered into flasks of 250 cc. capacity through several rather thick layers 
of absorbent cotton placed in a funnel. This filtration might well be done 
by placing the flasks in a steam sterilizer. If the filtrate is not clear, the 
liquid should be poured through the same layers of cotton till it does 
become clear. Care should be taken to keep the agar mixture hot during 
the filtering process ; otherwise the agar will not pass through the cotton. 
When the flasks are nearly full, plug the mouth of each with a large wad of 
cotton batting, put them into a steam sterilizer, and heat them at least 
thirty minutes on each of three successive days to make sure that all germs 
and their spores are killed. The flasks of agar may then be kept as a stock 
mixture until needed. 



BACTERIA AND HUMAN WELFARE 347 

Carefully clean and dry enough Petri dishes to supply, if possible, ten 
or more dishes for experiments with each division of students. Put the 
closed dishes in an oven and heat to a high temperature (150° C.) for an 
hour to kill any germs or spores that may be on the dishes. Allow the 
oven to cool before opening the door ; otherwise the dishes are likely to 
crack. 

To fill the Petri dishes, melt the agar mixture in a steam sterilizer ; 
then arrange the sterilized Petri dishes along the edge of a horizontal sur- 
face. Carefully remove the cotton plug from the flask, lift one edge of 
the cover of one of the Petri dishes, pour enough of the hot agar mixture 
into the lower part of the dish to make a layer about an eighth of an inch 
deep, and quickly replace the cover on the dish. Quickly pour into each 
of the dishes in turn. After the agar has hardened, the dishes are ready 
for the experiments. Any agar mixture left in the flasks should be steri- 
lized for thirty minutes on each of three successive days in order to make 
sure that it will keep for subsequent use. 

In general it is far more satisfactory to secure nutrient agar ready-made. 
City Boards of Health are usually glad to cooperate with biology teachers 
by furnishing this material. 

EXERCISE 59 

Are bacteria present in the air of the classroom? Laboratory 
demonstration. 

Materials and preparation: Two sterilized Petri dishes supplied with 
sterile nutrient agar. Remove the cover of one of the Petri dishes 
and expose the agar to the air of the classroom for ten minutes ; then 
cover the Petri dish, seal it with pasters, and label it Agar exposed 
to the air for ten minutes. Seal the second dish without opening it, 
and label it Agar not exposed to air. Place both dishes in a warm, 
dark place for about two days. The unopened dish is the control 
part of the experiment. 

1. Describe the preparation of each of the two dishes. 

2. Examine the agar exposed to the air. The tiny dots on the 
surface of the agar are known as colonies of bacteria. Each colony 
has developed from a single bacterium. Estimate the number of 
colonies present on the agar. Describe the shape and color of the 
various colonies. If fuzzy colonies appear in the dish they are mold 
colonies. 



348 PLANTS AND HUMAN WELFARE 

3. Examine the agar in the control dish and state whether or not 
colonies of bacteria are present. 

4. What is your conclusion as to the presence of bacteria in the 
air of the classroom? 

EXERCISE 60 

Are bacteria present in a given sample of milk? Laboratory 
demonstration. 

Materials and preparation: Dilute a small amount of milk with ten 
times its volume of water that has been recently boiled and then cooled. 
This sample of diluted milk should be kept in a sterilized test tube, the 
mouth of which is plugged with sterilized cotton. Two sterilized Petri 
dishes, each containing sterilized nutrient agar. 

Open both of the prepared Petri dishes. Over the surface of one of 
the dishes pour a few drops of the diluted milk and move the dish in 
such a way as to spread the milk evenly over the agar. Now close and 
seal both dishes with pasters. Label one dish Agar exposed to milk, 
and the other, Agar not exposed to milk. The latter is the control dish. 
The agar of this dish will enable you to tell about how many bacteria 
fell upon the agar from the air. Place both dishes in a warm, dark 
place for two days. 

1. Describe the preparation of the milk used and also the treat- 
ment of each of the two dishes. 

2. Why is sterile agar in sterilized dishes necessary in this experi- 
ment? 

3. Estimate the number of colonies of bacteria on the agar exposed 
to milk and state the number of colonies on the agar exposed to the 
air only. How many more colonies of bacteria are present on the 
agar exposed to milk than on the agar of the control dish? 

4. What is your conclusion as to the presence of bacteria in this 
sample of milk? 

EXERCISE 61 

Are bacteria present on the fingers, teeth, and hair? Laboratory 
demonstration. 

Materials and preparation: Secure three sterilized Petri dishes, 
each containing sterilized agar. Open one of the dishes and gently 
press the tips of two or more fingers on the surface of the agar on one 



BACTERIA AND HUMAN WELFARE 349 

side of the dish. Leave the agar on the other side of the dish as a con- 
trol. Cover and seal the dish and label it Agar exposed to the finger 
tips. 

Prepare a sterilized toothpick by sharpening the end of a match 
and passing it through a flame several times. Rub the tip of the 
toothpick between the teeth ; then open a second prepared Petri 
dish and make several scratches on the surface of the agar on one side 
with the tip of the toothpick that has been rubbed between the teeth. 
Leave the other side of the surface of the agar as a control. Seal the 
dish and label Agar exposed to matter from the teeth. 

Open the third prepared Petri dish and on one side of the surface 
of the agar drop several short hairs. Leave the other half of the 
agar untouched as a control. Seal and label the dish Agar exposed to 
hairs. 

Put the three dishes in a dark, warm place for two days. 

1. Describe the preparation of each of the three prepared Petri 
dishes. 

2. At the end of the two days examine the finger-tip impressions 
on the agar. 

a. State the number of colonies and irregular masses of bacteria 
present on the finger impressions. 

b. How many colonies are present in the control part of the agar 
outside the finger impressions ? 

c. What is your conclusion as to the presence of bacteria on your 
fingers ? 

3. Examine the scratches on the agar made by the toothpick. 

a. Give the number of definite colonies present, if any. 

b. Describe the appearance and extent of any continuous masses 
of bacteria in the cuts. 

c. State the number of colonies on the control part of the agar. 

d. State your conclusions as to the presence of bacteria on your 
teeth. 

4. Look at the surface of the agar where the hairs are in contact 
with it. 

a. Describe the extent of any continuous masses of bacteria, and 

i state where they are found. 

b. State the number of separate colonies, if any, in the similar 
situation as the masses referred to in 4a. 



350 PLANTS AND HUMAN WELFARE 

c. Give the number of colonies in the control part of the agar not 
touched by the hairs. 

d. What is your conclusion as to the presence of bacteria on the 
hairs ? 

EXERCISE 62 

Additional experiments with bacteria. 

1. Determine by the method used in Exercise 59 whether there 
are more bacteria in dusty air than in quiet air. 

2. Test the air in the street cars, subways, theaters for bacteria 
as in 1 above. 

3. Test various foods for bacteria, using the method outlined in 1 
above. 

4. Find out if there are more bacteria in a current of air produced 
by coughing or sneezing across an open Petri dish of sterilized agar 
than in a current of air produced by fanning the air across a second 
exposed dish of agar. 

EXERCISE 63 
How bacteria may be killed in wounds. Laboratory demonstration. 

Materials and preparation: Take two sterilized dishes each con- 
taining sterilized agar. Heat a dissecting needle in a hot flame to 
kill all the germs on it. After it has cooled, touch a colony of bacteria 
growing in one of the Petri dishes, and then transplant the bacteria 
thus obtained into one of the dishes by carefully raising the cover 
and making several scratches in the agar (for example, the date of the 
experiment or the number of the room). In a similar way prepare 
the second dish, and then pour over the cuts some iodine solution or 
other antiseptic. Seal each of the dishes. Label the first one Agar 
exposed to bacteria, and the second dish, Agar exposed to bacteria and 
treated with antiseptic. Put the dishes in a warm, dark place for two 
days. 

1. State what has been done to each of the prepared Petri dishes. 

2. What difference do you find at the end of two days in the 
appearance of the scratches made in the agar in the two dishes ? How do 
you account for the difference in the scratches in the agar of the two dishes ? 

3. What reason have you for thinking that bacteria in wounds in 
your body will be killed if an antiseptic solution like the one used in 
this experiment is put on the cut? 






BACTERIA AND HUMAN WELFARE 351 

Bacteria as the Foes of Man 

Injurious effects produced by bacteria. We have seen 
that most bacteria are either harmless or distinctly beneficial 
to man (pp. 341-342). Bacteria that cause decay and so 
increase the fertility of the soil become, however, the ene- 
mies of man when they feed upon the food materials used in 
our households. Every housekeeper knows that milk soon 
sours unless kept in a cold place and that meat and many 
other kinds of food quickly decay if they are not cooked or 
otherwise preserved. 

Unfortunately, too, there are certain bacteria, or germs, 1 
that find favorable conditions for growth in living tissues of our 
bodies and by their growth are the inciting causes of certain 
diseases, such as tuberculosis, diphtheria, and typhoid fever. 
Later we shall see that scientists are learning effective methods 
of preventing the ravages of these disease-producing bacteria, 
which we may well speak of as " man's invisible foes." 

Some methods of food preservation. We have seen that 
bacteria thrive whenever they can get plenty of food and 
moisture and whenever the temperature is favorable for 
growth. Common experience tells us, however, that if any 
one of these necessary conditions is wanting, bacteria cease 
to carry on their functions. If, then, we wish to keep food 
from spoiling, we need only to bring about conditions un- 
favorable for the growth of microorganisms. 

Meat, eggs, and other food materials will remain in a more 
or less fresh condition for a long time if they are put into 
cold storage. We find also that a high degree of heat will 

1 Disease-producing bacteria are commonly spoken of as germs, or microbes. 
These terms also include single-celled animals that cause disease. In general it is 
unnecessary and unwise for boys and girls to pay much attention to the symptoms 
and effects of disease. But since so much can be done to prevent these diseases 
that we have mentioned and others that afflict mankind, it is essential that the 
young should learn about some of these bacteria that are all too common. 



352 PLANTS AND HUMAN WELFARE 

kill bacteria, and so meats that have been cooked and milk 
that has been pasteurized or scalded will keep longer than 
when left uncooked. If meat, vegetables, or fruits are 
heated to the boiling point in cans and sealed up at once, 
they may be preserved almost indefinitely. 

Beef, ham, and fish are often smoked to preserve them, 
while pork and codfish are soaked in a strong solution of 
salt (brine) to keep them from the decaying action of bacteria. 
Another method of preserving food is by dehydrating, or 
taking away its water content. Dried beef, dried apples, 
hay, and seeds will keep indefinitely. Previous to the pas- 
sage of the Pure Food Law by Congress in 1906, many 
unscrupulous dealers were accustomed to use borax, formal- 
dehyde, and other chemicals in harmful quantities to prevent 
their food supplies from spoiling. 

Proper methods of sweeping and dusting. From our 
experiments in Exercise 62 we found that large numbers of 
bacteria are present in the air of rooms. These circulate 
where dust is raised by the movements of people or by sweep- 
ing. Since each of the colonies that we found on the Petri 
dishes usually starts from a single bacterium, it is easy to 
show the relative number of germs present in the air under 
varying conditions. 

The number of bacteria that may be found in a schoolroom, 
church, theater, or living room has been proved by a long 
series of experiments to be very considerable, for, with 
the ordinary methods of cleaning these rooms, very few of 
the germs are removed. When a room is swept, most of the 
light dust particles are raised from the floor and mingled 
with the air. After a short time the room is dusted, often 
with a feather duster. The bacteria that may have settled 
are then simply whisked off again into the air, without 
being removed from the room. 






BACTERIA AND HUMAN WELFARE 353 

Most of the germ-laden dust, however, can be removed 
from our homes if they are cleaned in a proper manner. In 
a room that has not been used for three or four hours prac- 
tically all of the bacteria and fine dust particles have settled 
out of the air upon the horizontal surfaces. For dusting, a 
cloth should be used, and never a feather duster. " Dustless 
dusters " may be bought, or they may be prepared by 
treating a piece of cheesecloth or flannel with a mixture of 
wax and turpentine. By the use of these cloths most of the 
particles of dust can be taken up and can then be removed 
from the cloths by washing them. If carpets, rugs, and 
draperies are then cleaned with a vacuum cleaner, practi- 
cally no dust is raised (111. p. 354 A) ; hence further dusting 
is unnecessary. 

It is much more hygienic to have floors covered with 
rugs than with carpets, for, if a vacuum cleaner is not avail- 
able, the dusty rugs and draperies can be removed from the 
room and cleaned in the open air. In general, a carpet 
sweeper is to be preferred to a broom as a means of cleaning 
carpets, since fewer germs are stirred up than when a broom 
is used (111. p. 354 D). Whenever brooms are used, small 
moistened bits of newspaper or tea leaves should be scattered 
on the floor before the sweeping is done. 

In the cleaning of public buildings the floors should first be 
sprinkled with moistened sawdust, and then the coarsest 
dirt should be swept up with bristle brooms. The floors 
should be washed frequently. Dirty streets, too, are a 
constant source of dust infection, unless they are kept moist 
while they are being swept. 

Proper methods of treating open wounds. A vast amount 
of physical discomfort and possible danger from bacterial 
infection would be avoided if people would use proper care 
in the treatment of wounds. When one cuts a finger or gets 




A B C D 

Photo by Elwin R. Sanborn 

Bacteria colonies resulting from different methods of sweeping 
Four rugs of the same size and approximately the same amount of use were selected, 
and placed at night in four different rooms. Early the next morning a Petri dish 
was uncovered in each room, and thus the nutrient agar of each dish was exposed 
to the air of the room for five minutes ; after which the dishes were covered (upper 
row of dishes). 

A second set of four dishes was then opened for five minutes while the four rugs 
were being cleaned as follows : rug A, with a vacuum cleaner (lower row of dishes) ; 
rug B, with a carpet sweeper; rug C, covered with pieces of wet newspaper and swept 
with a broom ; and rug D, with a dry broom. 

All eight dishes were closed and kept in a warm room for five days and then photo- 
graphed. The number of bacteria colonies in each dish were counted, and the results 
are expressed in the following table : 



No. Colonies 
before Sweeping 



No. Colonies 
after Sweeping 



No. Times Colonies 

Were Increased by 

Sweeping 



Dish A 
Dish B 
Dish C 
Dish D 



25 

7 
6 
4 



118 

135 

436 

1190 



4 

19 

72 

297 



BACTERIA AND HUMAN WELFARE 



355 



a sliver into the tissues, the finger becomes swollen and sore, 
and white " matter," or pus, often forms in the vicinity of 
the wound. These effects are largely due to the activity 
of bacteria which have been carried into the wound. Find- 
ing in the tissues all the favorable conditions for growth, 
these minute organisms multiply rapidly and produce poi- 
sons known as toxins, that cause the inflammation. 

The body, however, has a very efficient means of protec- 
tion. The blood in addition to red corpuscles has a rela- 
tively smaller number of white 




A white corpuscle destroyed by bacteria 




A white corpuscle devouring a bacterium 
White corpuscles and bacteria 



corpuscles. These have very 
important functions. As soon 
as the inflammatory processes 
that we have been describing 
begin in the wound, large 
numbers of white corpuscles 
from all over the body are 
hurried to the spot and be- 
gin to attack the invading 
bacteria. If the number of germs is relatively small and their 
virulence not excessive, and if the corpuscles are in a healthy 
condition, these cells of the blood seize upon and devour 
the bacteria. Under these conditions little, if any, pus is 
formed. But if the bacteria get the upper hand in the 
struggle, many of the white corpuscles are killed, and it is 
the dead corpuscles that form the pus (111. above). 

A cut should be allowed to bleed rather freely to remove 
the bacteria that may have been brought in. The wound 
should then be covered with a sterile bandage. Wounds 
in which the bleeding is slight should be treated as soon as 
possible with iodine solution or other germ-destroying (anti- 
septic) solution. When iodine solution is used, it should 
be washed off with alcohol, in order to prevent the iodine 



356 



PLANTS AND HUMAN WELFARE 



from burning into the tissues. A sterile bandage should 
then be applied to prevent the entrance of germs. With 
proper treatment a wound should show no sign of inflamma- 
tion or of the formation of pus, and should heal rapidly. 
Cause of tuberculosis. Formerly one seventh of all 
the deaths in the world were due to tuberculosis, more com- 
monly known as consumption. Even to-day, in New York 



im 

Deaths per 100,000 

population 

200 



-^ 



1930 

Deaths per 100,000 

population 

71.5 



V 



Courtesy of National Tuberculosis Association 

The decline in death rate from tuberculosis 
What difference in the death rate in 1904 and 1930? Give as many reasons as you 

can for this decline. 

City the Board of Health reports 200 to 300 new cases each 
week. Yet, if the general public only knew the manner in 
which this disease is transmitted and would make use of this 
knowledge, the dreadful sacrifice of life and health due to 
this " great white plague " could be almost wholly prevented. 
In 1882, Dr. Robert Koch (koK), a noted German scientist 
(111. p. 358), proved that tuberculosis is always caused by 
extremely small rod-shaped bacteria. He found countless 






BACTERIA AND HUMAN WELFARE 357 



numbers of these living germs in the sputum coughed up 
by consumptive patients. He cultivated these germs 
(111. p. 359) in test tubes ; and when he injected the bacteria 
into the bodies of guinea pigs or rabbits, the animals became 
ill with tuberculosis, and the germs were always found 
present in the bodies of these animals. 

We are absolutely sure, therefore, that before anyone 
can become a consumptive, he must take into his body the 

The dangerous age 

15 to hS 




Under 5 years 100 years and over 

Courtesy of National Tuberculosis Association 

The period most dangerous in tuberculosis 
On a piece of paper divide the space between the vertical lines into six equal spaces 
(each representing five years), and thus determine about the age when tuberculosis is 
most common. 

living bacteria of tuberculosis, the more common avenue 
of infection being through the mouth, nasal, and other air 
passages. When the bacteria get into the lungs of a person 
who happens to be a " little run down," as we say, straight- 
way the bacteria begin to multiply, feeding meanwhile on 
the tissues of the lungs. If the malady is not arrested, the 
lungs may gradually be destroyed. For this reason the 
disease is called consumption. The bacilli cause the forma- 
tion of tiny nodules of inflammation. These ulcerate, 



358 



PLANTS AND HUMAN WELFARE 



that is, the tubercle bacilli cause the destruction of body- 
tissue, and the ulceration usually opens into one of the air 
spaces in the lung. The material thus poured into the 
air space sets up an irritation, a cough results, and the person 
expectorates. Inasmuch as this material contains enormous 
numbers of living tubercle bacilli, the coughed-up sputum is 
highly dangerous. The tiny inflammatory nodule is spoken 

of as a " tubercle." In per- 






1 



f 




sons dying of consumption, 
the lung is studded with 
countless thousands of such 
tubercles, hence the name 
"tuberculosis." 

From what has been said 
it is clear that the coughing 
and spitting consumptive is 
the great source of danger. 
Moreover, since infants and 
young children have little or 
no natural resistance to the 
germs of tuberculosis, it is 
clear that they are particu- 
larly endangered if some 
adult member of the family 
has tuberculosis. 
At one time it was thought that the milk coming from 
tuberculous cows was also a source of pulmonary tubercu- 
losis. We now know that this is not true. The tubercle 
bacilli coming from diseased cows are a source of danger 
to infants and children, but they give rise to tuberculosis 
of the intestinal tract and of the bones, joints, and glands. 
Pulmonary tuberculosis appears to be caused only by the 
tubercle bacilli coming from human sources. 



Photograph by Army Medical Museum 

Dr. Robert Koch (i 843-1 910) 






BACTERIA AND HUMAN WELFARE 



359 



Some precautions that tuberculous patients should take. 

Consumptives, through ignorance or carelessness, frequently 
cough into the air a fine spray containing the living germs 
of tuberculosis, and anyone in the vicinity of the patient 
may inhale these virulent germs. It is of the utmost im- 
portance, therefore, that these living germs be kept out of 
the bodies of people who come in contact with consumptives. 
Responsibility in this 
matter rests very largely 
upon the patients them- 
selves; and if they ex- 
ercise the necessary care, 
they need not become a 
menace to healthy 
people in the home or 
the community. It is 
of course essential that 
every effort be made to 
stop the filthy and dan- 
gerous habit of spitting. 
Many people have the 
disease long before they 
are aware of it, and a 
general public sentiment 
should be developed that will actively assist boards of health 
in enforcing their rules against the spitting nuisance. Every 
consumptive should expectorate in paper cups, which should 
be burned. 

Tuberculous patients should exercise great care not to 
cough or sneeze without covering the mouth or nose with 
the handkerchief, for it has been proved that living germs 
are widely distributed by carelessness in this regard ; in- 
deed, this should be a general rule with every one. Separate 




Courtesy of National Tuberculosis Association 

Bacteria of tuberculosis 

To which of the three classes of bacteria shown 

on page 342 do these belong ? 






360 PLANTS AND HUMAN WELFARE 

knives, forks, spoons, and drinking vessels should be set apart 
for consumptives, and these should be sterilized in boiling 
water after they have been used. Kissing on the lips, es- 
pecially of children, should never be permitted, for this is a 
frequent cause of infection. In order to prevent the trans- 
mission of tuberculosis from infected cattle, all milk should 
be pasteurized. When this is not feasible, and raw milk 
must be used, the milk should be obtained only from cattle 
which, as the result of tuberculosis tests, are known to be 
free from tuberculosis. Raw milk, can, of course, be heated 
in the home. This, in fact, is the common practice in Euro- 
pean countries. 

Some methods of treating tuberculous patients. In 
former years the decision by doctors that a patient had 
tuberculosis was believed to be a sentence to a lingering 
death. It was believed, also, that this disease is hereditary. 
Happily modern medicine has dispelled both of these illu- 
sions. A child may inherit weak lungs or a frail body ; but 
he will never be a consumptive unless the bacteria that cause 
this disease are in some way planted in his tissues. Con- 
sumption is a curable disease, unless it is neglected until it 
has reached an advanced stage. The prime requisites in the 
treatment of the disease are rest, a plentiful supply of fresh 
air, and a well-balanced diet of easily digested and nutritious 
food, and freedom from muscular work and from worry. 

What the individual can do to protect himself against 
tuberculosis. It must be evident from the foregoing dis- 
cussion that the chances of exposure to the germs of tuber- 
culosis are very great. Indeed, those who have examined 
the lungs of people who have died of other diseases maintain 
that a very large proportion give evidence of areas that 
have been attacked by tuberculosis germs. X-ray pictures 
frequently indicate the same in the case of healthy people. 



BACTERIA AND HUMAN WELFARE 



361 



We naturally ask why, in these cases, the disease did not 
progress sufficiently to become apparent. The answer is 
that the body cells were able to overcome and so to stop 
the further progress of these destructive germs. One can 
see, therefore, that vigorous health of the individual is of 




Courtesy of National Tuberculosis Association 

A tuberculosis sanitarium 
Note the happy faces of the patients who are taking the rest treatment. 

supreme importance in avoiding tuberculosis. To secure 
abounding health, young people and old alike should eat 
plenty of nourishing foods, should exercise in the open air, 
get sufficient sleep in well-ventilated rooms, and endeavor 
always to look on the bright side of life. Very young chil- 
dren should be prevented from coming in contact with tuber- 
culous people, for even when in the best of health, they often 
become infected. Later, if they are weakened by other 



362 PLANTS AND HUMAN WELFARE 

diseases, the germs of tuberculosis which they have taken 
in may become active, and the disease may develop. 

The cause and treatment of diphtheria. Another disease 
that formerly claimed many victims, especially young chil- 
dren, is diphtheria. The germs of this disease are rod-shaped 
(bacilli), somewhat larger than those that cause tuber- 
culosis, and when properly treated with stains, show cross 
stripes. When these bacteria find lodgment and grow in 
the throat, they produce a membrane and form a poisonous 
substance, or diphtheria toxin, which is absorbed and carried 
by the blood. 

The cells of the body, however, at once set to work to 
produce substances that will neutralize or overcome the 
toxins formed by the diphtheria bacillus ; these substances 
are known as diphtheria antitoxins. If the amount of toxin 
produced by the diphtheria bacilli is very great, or if it is 
particularly powerful, the cells of the body, especially the 
very delicate nerve cells, will be seriously injured and the 
patient will die, usually from paralysis of the heart. In 
other cases the body cells gradually produce sufficient anti- 
toxin to neutralize completely the poison, and the patient 
recovers. 

In 1892 a most important discovery was made by a Ger- 
man bacteriologist, Von Behring. He found that it is not 
necessary for the human body to manufacture all the anti- 
toxin it needs for its struggle with the diphtheria poisons, 
since this substance may be taken from the blood of other 
animals which have been producing it. For this purpose, 
healthy horses are now secured by city boards of health, 
and a small dose of diphtheria toxin is injected into their 
bodies. At intervals of five to seven days these injections 
are repeated, the dose of toxins being gradually increased. 
At the end of several months of this treatment, the animals 



BACTERIA AND HUMAN WELFARE 



363 



can stand a quantity of the poison, a thousandth part of 
which would probably have proved fatal if given at an 
earlier time. For during all these days, each horse has been 
having a mild form of diphtheria, and the cells of his body 
have been producing and giving into his blood an amount 




Securing antitoxin 



Photograph by A. Tennyson Beals 



This horse during its lifetime supplied antitoxin valued at over $100,000. 



of antitoxin much more than is needed to neutralize the 
diphtheria poisons which the animal has been receiving. 
Some of the blood is then carefully removed and allowed to 
clot (111. above). The liquid serum that oozes out of the 
clot contains the antitoxin, and it is this serum properly 
prepared which is injected into human beings when diph- 



364 PLANTS AND HUMAN WELFARE 

theria attacks them. And so our good friend the horse, with 
no permanent ill effects to himself, has decreased the death 
rate formerly caused by diphtheria, until now it is a very 
small fraction of what it used to be. 

Prevention of diphtheria. It is much more important 
to prevent attacks of this disease than it is to know how to 
cure it. So again we find strong arguments for the enforce- 
ment of rules against spitting, for living bacteria of diphtheria 
are often found in the throats of those who are thought to 
have ordinary sore throats. For this reason, too, the mouth 
and the nose always should be covered when one coughs or 
sneezes. Children should be especially careful not to put 
into their mouths pencils, coins, or other objects that have 
been used by others, for diphtheria germs have often been 
transmitted in this way. 

In spite of all precautions that may be taken, because 
of crowded conditions among human beings or close con- 
tact, children are likely to be exposed to diphtheria germs 
that have been forced into the air by sneezing or coughing. 
Diphtheria antitoxin may be administered to any members 
of the family who have been exposed to diphtheria ; it then 
becomes a means of preventing the disease, but this protec- 
tion is found to last only a few days. 

When a disease like diphtheria becomes epidemic, some 
people never take it since they have a natural immunity. 
In some diseases, such as smallpox, measles, and scarlet 
fever, one attack usually renders a person safe from a recur- 
rence. This is not true, however, of diphtheria. Fortu- 
nately, a method known as the Schick test (111. p. 365) has 
been discovered which enables a physician to determine 
whether or not a child is naturally immune. If it is found 
that he is not immune, a dose of toxoid or diphtheria toxin- 
antitoxin, is injected. Toxoid is prepared by treating 



BACTERIA AND HUMAN WELFARE 



365 



diphtheria toxin with formalin for a month. Thus the child 
is protected from infection for a number of years and 
probably for life. More than 500,000 children living in 
New York City have received this protective, or immunizing, 
treatment within the past two years. At one time such 
immunizing treatments were given only to children who, 




Photograph by A. Tennyson Beals 



The Schick test 
Note that the children seem wholly unafraid. 

as a result of a Schick test, had been shown to be susceptible 
to diphtheria. Nowadays, however, since it has been 
established that almost all young children about one year 
of age are susceptible, the treatments are usually given to 
all infants without a previous Schick test. 

The cause of typhoid fever. This disease also is caused 
by the growth in the body of rod-shaped bacteria of a def- 



366 



PLANTS AND HUMAN WELFARE 



inite kind. These typhoid bacteria have hairlike projections 
which vibrate rapidly and so enable the germs to move 
about (111. below). The bacteria of typhoid fever are practi- 
cally always taken into the body through the mouth and 
thence into the intestines. Food and drink are the vehicles 
which serve for the entrance of the bacilli ; water and milk 

are probably the most 
frequent sources of in- 
fection. Milk is es- 
pecially dangerous 
from the fact that 
typhoid bacteria not 
only live but multiply 
in it. Water and milk 
are dangerous, how- 
ever, only when they 
actually contain the 
typhoid bacteria 
which have entered 
into them commonly 
from the intestinal or 
kidney excretions of 
typhoid patients. It 
has been proved over 
and over again that the common house fly may also be the 
means by which typhoid fever is transmitted. These in- 
sects often alight on the excrement of typhoid patients and 
then carry the germs on their sticky feet (111. p. 508), and so 
they infect the foods on which they alight. 

The prevention of typhoid fever. If the excrement from 
the intestines and the kidney secretions of typhoid patients 
were thoroughly disinfected by heat, carbolic acid, or other 
germicides, the spread of typhoid fever would be very largely 




Courtesy of Dr. William H. Park 

The bacteria of typhoid fever 

How do these bacilli differ from any of the bacilli 

shown on page 342 ? 



BACTERIA AND HUMAN WELFARE 367 

prevented. However, the bacteria of this disease may con- 
tinue to live and to multiply in the gall bladder or kidneys or 
intestines of some people who have had typhoid fever, even 
years after recovery from the disease. These people are 
called typhoid carriers. Their bowel excrements, sometimes 
their urine, contain enormous numbers of living typhoid 
bacilli. Epidemics of typhoid fever have frequently been 
traced to typhoid carriers. We can see, then, how important 
it is that boards of health make a careful inspection of those 
who handle foods. All typhoid carriers should be barred 
from such occupations. 

One of the most difficult problems that formerly con- 
fronted armies was that of preventing typhoid infection. In 
the Mexican War and in the Civil War the armies on both 
sides paid frightful toll to this dread disease. Even in the 
Spanish-American War five thousand men in the United 
States army died of typhoid fever or other water- or fly- 
borne diseases, while only three hundred were killed by 
Spanish bullets. Since that time, however, sanitary camps 
with pure water supply and means of preventing the breed- 
ing of flies have greatly improved conditions. In recent 
years an antityphoid vaccine, consisting of dead typhoid 
germs, is injected as a means of prevention. The results 
of the use of this vaccine have been most favorable. The 
general improvement in army health is strikingly shown by 
comparing figures for two army divisions of about the same 
size, one at Jacksonville, Florida, during the Spanish- 
American War in 1898, and the other at San Antonio, 
Texas, during the 1911 maneuvers on the Mexican border. 
(See table on page 368.) 

In the World War all our soldiers and sailors received the 
antityphoid treatment, with the result that the disease was 
rare indeed. 



368 



PLANTS AND HUMAN WELFARE 



Number of soldiers 

Number of cases of typhoid (certain and 
probable) 

Number of deaths from typhoid fever . . 
Number of deaths from all diseases . . . 



San Antonio 
1911 




Safety of water supplies. In country districts, each house 
usually has its own well, and so the family becomes account- 
able for its own water supply. In this case great care should 
be taken to place the well in such a position that none of the 
drainage from the house or barn can soak through the porous 
soil into the well. Those who live in large towns or cities 
almost always obtain their water supply from a common 
source. This sometimes becomes contaminated by typhoid 
or other disease germs, and a disease epidemic is likely 
to follow. An emergency water-purification plant can then 
be installed by the State Board of Health. A sufficient 
quantity of chlorine is then added to the water to destroy all 
dangerous foreign matter. If this cannot be done, boards 
of health should notify the householders, and the water, 
when used for drinking purposes, should be boiled and kept 
on ice until used. 

Safeguarding milk supplies. Families in rural communi- 
ties who keep cows can be sure of clean milk only if they take 
the necessary care. Cows need plenty of light, air, whole- 
some food, and clean surroundings. If any of these is want- 
ing, the animals are likely to become diseased, and the milk 
is then affected. In sanitary dairies great care is taken at 
milking time to see that the surface of the body of the cow, 
especially about the flanks and udders, is brushed and then 



BACTERIA AND HUMAN WELFARE 369 

wiped with a moist cloth and that the hands and clothing 
of those who do the milking are kept clean (111. below). 

No one who has an infectious disease should be permitted 
to have anything to do with the care of cows or of the milk. 
Over and over again epidemics of diphtheria, scarlet fever, 
typhoid, and of tuberculosis in infants have been traced 









'ji^SSSH 


*"' ■'?.■■■'■'■'«-.■■■■■ '.- 




*4^ , 4 1i vS 




■ .*# I 


J»w £&$!mr*!iL 


i^flPf&i 


r l^j^ 




**^^M wHKU- y 


j^SsST s^ r ;;; |r 




Hr^t;iij 


mk i, 




ir dwm # f y ^- 


W 




^1 lil J WKl 


< 



Courtesy of Walker-Gordon Laboratory Company, Inc. 

A sanitary dairy 
Fifty cows at one time are upon this revolving platform known as a rotolactor. The 
bodies of the cows are carefully cleaned, the milking tubes are attached, milking is 
done by machinery, the tubes are sterilized, and then the cows return to their barns. 
The whole time required for each cow is only 12^ minutes. 

along the routes of careless milkmen. At the present time 
public health authorities test cattle to see that they are free 
from tuberculosis. The diseased cattle are killed. 

Those who live in cities are wholly dependent for milk 
upon sources they know nothing about. The milk that is 
consumed in New York City, for instance, comes from 
over 40,000 dairies, scattered through six different states. 



370 



PLANTS AND HUMAN WELFARE 




It is, of course, impossible to make constant inspection in 
such a wide field. The New York Board of Health is doing 
all it can in this respect, and as far as possible it prevents 
dirty and dangerous milk from being sold. The only path 

of safety lies in the 
careful pasteuriza- 
tion of milk and 
cream that are used 
for drinking pur- 
poses, especially by 
young children. In 
communities where 
pasteurization is in- 
sisted upon, there 
has been a surpris- 
ing decrease in the 
percentage of sick- 
ness and deaths 
from intestinal dis- 
eases, especially in 
the summer time 
and among young 
children. If the only milk obtainable is of a doubtful qual- 
ity, it can be made safe by bringing it nearly to the boiling 
point for a few minutes. 

Smallpox and vaccination. Smallpox was once exceed- 
ingly common. It was introduced into America by the 
Spaniards ; it destroyed 3,500,000 people in Mexico and 
spread with frightful rapidity throughout the New World, 
until in 1733 it nearly depopulated Greenland. Mankind 
is indebted to Dr. Edward Jenner (111. p. 372), an English 
physician, who in 1796 proved that vaccination is a sure 
method of preventing the disease. In vaccination our bodies 



Courtesy of Walker-Gordon Laboratory Company, Inc. 

Counting bacteria in milk 
The Petri dish containing the milk sample is placed 
over a black surface divided into spaces by white lines. 
With the help of a magnifier the examiner counts the 
colonies in the various spaces and records each colony 
by means of the automatic counter in his left hand. 



BACTERIA AND HUMAN WELFARE 



371 



receive germs which probably in the distant past came from 
smallpox, but which have been so modified that they cause 
a mild form of disease (cowpox) very different from smallpox 
itself. The cells of the body produce some form of pro- 
tective substance which is an effective safeguard when we 
are exposed to the disease. This kind of protection does not 




Courtesy of Walker-Gordon Laboratory Company, Inc. 

Bottling certified milk 
Note that the hands of the workmen do not come in contact with the milk. 

last indefinitely, however, and every person should make 
sure that successful vaccination is performed at least once 
in ten years, and oftener than that if cases of small- 
pox develop in the community in which he is living. If 
a person has actually been exposed to the disease, he should 
be vaccinated immediately. Since the introduction of com- 



372 



PLANTS AND HUMAN WELFARE 






pulsory vaccination, smallpox is becoming comparatively 
rare. 

Hydrophobia and the Pasteur treatment. Hydrophobia, or 

rabies, is a disease due to the bite of a mad dog, cat, or wolf. 

,.._ : - ... .. Until the latter part 

of the nineteenth 
century, the only 
known method of 
treating this dis- 
ease was that of 
burning out, or 
cauterizing, the 
wounds with hot 
irons or nitric acid. 
After a long series 
of investigations, 
however, Louis 
Pasteur, the French 
scientist, made 
known to the world 
the so-called Pas- 
teur treatment 
(1885). Pasteur 
found that the dis- 
ease was located in 
the spinal cord and 
that, if pieces of 
the spinal cord of 
a rabbit which had 
died of hydropho- 
bia were allowed to dry in the air, the germs gradually lost 
their virulence. He therefore began the treatment of patients 
who had been bitten by mad dogs by injecting beneath the 




Photograph by Army Medical Museum 

Dr. Edward Jenner (i 749-1 823) 
This statue portrays Dr. Jenner vaccinating his own 
son. His discovery has saved millions of people from 
an untimely death and still other millions from disfigure- 
ment. 



BACTERIA AND HUMAN WELFARE 373 

skin an emulsion made from the spinal cords which had been 
dried for fourteen days. Each day for twenty-one days an 
injection was made from a cord that had been dried for a 
shorter time, until finally injections were made of a cord 
dried only a few days. Now the vaccine is prepared by 
heating the spinal cords or by treating them with carbolic 
acid so that the vaccine is absolutely safe. Since, fortu- 
nately, hydrophobia usually does not develop in human 
beings for two weeks to four months after the bite of a mad 
dog, the cells of the body, by this Pasteur treatment, grad- 
ually acquire the power to resist the hydrophobia toxins, 
and so the disease is prevented if the wound is cauterized 
at once and treatment begun immediately. The cauteriza- 
tion is of value, however, even after a delay of twenty-four 
hours, but it must be thorough, and be done with concen- 
trated nitric acid. If necessary, an anaesthetic should be 
given. 

Safeguards of the body against disease. In the first place, 
the tough outer skin, as long as it is unbroken, forms a most 
effective barrier to the entrance of bacteria. The mouth 
and nose openings are a constant source of danger. Each 
of the nostrils is guarded by hairs that collect many dirt 
particles. On the mucous membrane lining the nose and 
throat, still other bacteria are caught. The cells which line 
the windpipe are furnished with cilia which lash upward 
(111. p. 174) and help expel the germs that may have gone past 
the outer lines of defense. If the bacteria enter the stomach 
and the intestines in a living condition, many of them are 
destroyed by the acid gastric juice. Finally, should the in- 
vading microbes reach the interior of our lungs, our muscles, 
or our brain, we can still rely upon the antitoxins, or other 
protective substances, which the cells of a healthy human 
body are ever ready to produce. In such contagious diseases 



374 PLANTS AND HUMAN WELFARE 

as smallpox or scarlet fever, these protective substances 
remain for a considerable time in the blood, to make us 
immune against a second attack. The white corpuscles 
are ever ready to pounce upon the bacteria, either to 
devour them or to carry them off from the body. An opti- 
mistic view of life and freedom from worry are undoubtedly 
very important factors in keeping the body in a state of 
vigorous health. A happy way of looking at life acts on the 
body somewhat like oil on the working of machinery. Oil 
prevents friction in a machine. Optimism enables the body 
to carry on its work more smoothly. 

Bacteria as the Friends of Man 

Bacteria and soil fertility. The action of bacteria in caus- 
ing decay. Were it not for the never-ending activity of bac- 
teria, all life upon the earth would soon cease to exist. Let 
us see why this is true. When animals or plants die, their 
bodies fall upon the ground ; and were not these lifeless 
masses taken care of, the whole surface of the earth would 
be covered with a vast number of unburied organisms. All 
this dead material is food for countless bacteria. They cause 
it to decay and thus decompose it into simpler chemical 
compounds that soak into the earth and serve as nutriment 
for the higher plants. Since plants are constantly taking 
from the earth the materials that they need to make food 
substances, this soil would tend to become less and less 
fertile, were it not for the work of the bacteria that cause 
decomposition. This is one reason why rotting manure 
adds to the fertility of the soil. 

The action of nitrogen-fixing bacteria. It has been proved 
that certain kinds of bacteria directly increase the amount 
of nitrogen compounds that are so essential in the soil for 
plant growth. It has long been known that corn and other 



BACTERIA AND HUMAN WELFARE 



375 



2 
O 

s 
o 

u 



-«-o 



la 

O O 

2 & 
3<J 






o 

b « 

< **■ 

n w 

5 H 

< K 






h * b 

2£? 



w 03 o3 a ■« 
°n_- > OJ 

Sill- 

^.2-0 o3 a> 



a> 



»d 

oj o3 

£" 3 



0) 03 



85 «| 

lip 



343 o3 



9 S ft-- 

-5 ST*© 

. - CO 



i i aT 2 



m ~ ;n _d 



I1S-8J 

ft S-ft o 

II ill 

'S « o 



"flog d-£ £ 



T3 e8 O 

a 9 m 



o p"3 



O CO m 

sis 



a _j d 

jj< >> 2 S 

■gfl g -5 a 

o3 ««-*h S3 -"S-^ 

et,o°d £ o 

£ » o* c 3 

° 5 ft d •- ,2«i 

. f OQ41 «P 

r 1 "-k3'J3 d c3 £ 

as >> o «•« d CD 

-3=3 =1 oi § :g M 

GO K* 



d 

03 g 

|» 

d o 
i-h 



-ft O o3 h 



CO fcj ' 

® « 

ft 2 



31 



5 s| s § 
&JW°1 

d 2 m c « 

O o d ^ -Q 



« 2 



13 -r 



a 

CO 

C 
03 

03 O 



— 0> 
«*5 o3 oo 

ft CB 

» d.2 

pq 



03 

I & 

3 J- 



376 



PLANTS AND HUMAN WELFARE 



^Animal _ 
> proteins" 



crops will grow better in soil that has previously borne a crop 
of beans, peas, clover, or other members of the pod-bearing 
family. Within recent years an explanation of this fact has 
been found. When the roots of these pod-bearing plants are 
examined, small swellings, or tubercles, are seen (111. p. 377). 
These tubercles contain multitudes of bacteria that are able to 

take the free nitro- 
gen from the air be- 
tween the particles 
of the soil and to 
combine it with so- 
dium or potassium 
oxids, thus forming 
sodium and potas- 
sium nitrates, which 
are very important 
minerals needed by 
all crops. Since 
these nitrogen-fixing 
bacteria can be 
planted in soils that 
do not have them, 
it is possible to restore in this way much of the fertility 
that may have been lost (111. above). 

Bacteria and the flavors of food. Many flavors of food are 
due to the action of bacteria. The flesh of cattle that have 
just been killed is often tough and tasteless. If allowed to 
stand, however, these meats become tender and acquire their 
distinctive flavors by the decomposing action of bacteria. 

A similar action takes place when butter or cheese ripens, 
and the dairy industry has been perfected to such a degree 
that bacteria of certain kinds have been proved to give rise 
to definite flavors. These bacteria are produced in pure 




Nitrates Ammonia 



Nitrogen-fixing 
bacteria in nodules 



Nitrogen 
atmosphere' 

The nitrogen cycle 
Beginning with plant proteins name in order the va- 
rious steps through which nitrogen passes as repre- 
sented (a) in the outer circle, (b) in the inner circle. 



BACTERIA AND HUMAN WELFARE 



377 



cultures for the dairyman by growing them on food sub- 
stances in test tubes. They are then transplanted into 
the milk. 

Bacteria and 
the industries. 
Without the help 
of bacteria, the 
preparation of 
the fibers of flax 
(linen), jute, 
and hemp would 
be impossible. 
These plant fibers 
are connected 
with the woody 
materials of the 
plants so closely 
that they cannot 
be separated un- 
less the stems of 
flax, hemp, and 
jute are first sub- 
jected to a proc- 
ess of decay in 
large tanks, or in 
streams of water. 
Moisture and 
warmth induce the rapid growth of bacteria ; the resulting 
decay of the softer cells loosens the tough fibers so they can 
be separated from the useless parts of the plant. The change 
of alcohol to vinegar is also caused by bacteria. Millions of 
bacteria known as " mother of vinegar " are found in the 
jellylike mass at the bottom of a vinegar bottle or barrel. 




Courtesy of Brooklyn Botanic Garden 

Nodules containing nitrogen-fixing bacteria on the 
roots of the soy-bean plant 



378 PLANTS AND HUMAN WELFARE 

QUESTIONS AND APPLICATIONS 

1. What is meant by the germ theory of disease? 

2. Describe three shapes of bacteria, and give the scientific name of 
each of the types. 

3. How are some bacteria able to move about? 

4. Why were bacteria unknown before Leeuwenhoek began his investi- 
gations ? 

5. Give some idea of the rapidity with which bacteria may reproduce. 
What conditions tend to check this rapid multiplication of bacteria? 

6. Why will boiling water fail to kill some bacteria? 

7. How are Petri dishes prepared for experiments with bacteria ? 

8. What is meant by colonies of bacteria ? Describe the shape, color, 
and luster of bacteria colonies which you have seen. 

9. Why were you certain that the bacteria in the agar exposed to the 
air or milk came from the air or milk ? 

10. What observation did you make in Ex. 63 that led you to conclude 
that the germicide used had killed the bacteria transplanted in the agar? 

11. What produces the inflammation and pus in a cut? Of what is pus 
composed ? How may both inflammation and pus be prevented ? 

12. Should bleeding from a cut be stopped at once ? Explain. 

13. Why should a sterile bandage be used in case of any but very slight 
scratches ? 

14. How did Dr. Koch prove that a certain kind of bacteria caused 
tuberculosis ? 

15. Since one can scarcely expect to escape exposure to the germs of 
tuberculosis, what are the best methods to employ to prevent one's getting 
the disease? 

16. What are four requisites in the treatment of tuberculosis? 

17. Define toxin, antitoxin, toxin-antitoxin, toxoid, and show how each 
of these terms applies to diphtheria. 

18. What is the use of the Schick test? 

19. How may typhoid fever be prevented (a) by sanitary measures; 
(6) by vaccination ? 

20. How does smallpox vaccine differ from typhoid vaccine ? 

21. How does the vaccine now used in the treatment to prevent hydro- 
phobia differ from that used in the earlier Pasteur treatment? 

22. What changes do the bacteria of decay make in dead plants and 
animals that help to make soil more fertile ? 



BACTERIA AND HUMAN WELFARE 379 

23. Where do nitrogen-fixing bacteria live, and what do they make? 
What is the use to plants of the compounds formed? 

24. State the source of each of the elements in the compounds formed 
by nitrogen-fixing bacteria. 

25. In what other ways are bacteria useful? 

26. What is meant by certified milk ? Why is this so much more expen- 
sive than raw milk that is pasteurized ? 

27. Make an investigation of your water supply. How is the supply 
examined and protected? 

28. Find out all you can about the duties of the Board of Health of 
your town or city. 

29. What common beliefs as to the cause of sickness, other than those 
mentioned on pages 340-341, have you heard or read about? 

30. Study the advertising columns of newspapers and magazines and 
bring to class as many advertisements as possible that relate to the cure 
of disease. Consider carefully whether you or your family would be wise 
to purchase or use the remedies mentioned in the advertisements. 

31. Ask your teacher to secure from the Metropolitan Life Insurance 
Company, 1 Madison Avenue, New York City, a single copy of each of 
the following fascinating pamphlets on "Health Heroes" : Louis Pasteur, 
Edward Jenner, Edward Livingston Trudeau, Florence Nightingale, 
Walter Reed, and Robert Koch, and other health pamphlets designed 
for class use. How can this company and other great life-insurance 
companies afford to supply the public without cost all this valuable in- 
formation they send out? 

32. Visit a sanitary dairy plant. Enumerate all the provisions that 
have been made, with respect to the cows and the milkers, for securing 
comfort of the cows and milk with a low bacteria content. 

33. Pay a visit to a pasteurization plant. Describe the steps taken 
from the time the raw milk is received until it is delivered to the con- 
sumer. 

34. Secure from your local or state Board of Health a copy of the 
weekly, monthly, or annual report on the prevalence of various kinds of 
diseases. Which diseases do you find very common? Determine the 
months in the year when certain diseases are most prevalent. Can you 
suggest any reason for this? Which diseases seem most likely to result 
in death? If possible, find out the years in which certain diseases (e.g. 
infantile paralysis, grippe) were especially epidemic. 



UNIT IX. ANIMALS AND HUMAN WELFARE 

PROBLEM 1. HOW ARE ANIMALS CLASSIFIED? 



Scientific Methods of Classifying Animals 

Similarity of structure as a basis for classifying animals. 

Vertebrates. The scientific classification of animals as 
well as that of plants is based on structure. The more 
nearly two animals are alike in structure, the more closely 

they are believed to be re- 
lated. However, many ani- 
mals which are quite differ- 
ent in structure in many 
respects may have one or 
more common, but funda- 
mental, characteristics of 
structure. Thus such di- 
verse forms of life as a 
perch, a frog, a turtle, a 
bird, and a man all possess 
an internal bony skeleton 
(111. p. 561), one of the prin- 
cipal parts of which is a series of bones joined together to form 
what is known as the spinal column. The bones in the spinal 
column are called vertebrce, hence all such animals are known 
as vertebrates. The vertebrates constitute a group of animals 
known as a Branch or Phylum (fi'lflm) of the animal king- 
dom. The vertebrates are subdivided into groups known 
as Classes of vertebrates. The vertebrates which we have 

380 




Photograph by Cornelia Clarle 

A spider 

Give one reason why the spider cannot 

be classed as an insect. 






ANIMAL CLASSIFICATION 



381 



studied, or shall study, are grouped under the following 
classes : Mammals, birds, reptiles (turtles, snakes, and 
lizards), amphibians (frogs and toads), fishes. 

Invertebrates. All animals that have no internal bony 
skeleton are, for convenience, called invertebrates, that is, 




Courtesy of American Forests and Forest Life 

A spider's web 
This was made by an orb-weaver. The material for the web comes from the tip 
of the abdomen and not from the mouth region as is the case with caterpillars. (See 
111. p. 477.) 

animals without vertebrae. But a negative characteristic, 
that is, a peculiarity of structure that a group of animals 
does not possess, cannot be of much use in determining the 
relationship of these animals. Thus, the single-celled ani- 
mal, the amoeba (111. p. 211), and the house fly (111. p. 509) 
are both invertebrates. Evidently these animals are not 






382 



ANIMALS AND HUMAN WELFARE 



at all closely related, since they have so little in common. 
Biologists have found that the invertebrate animals may 
be divided into ten or more branches, each of which will 
include the animals that are structurally alike in several 
fundamental respects. Let us now consider one or more of 
the prominent characteristics of each of six of the branches 
of the invertebrates. 

Arthropods. The first branch we shall discuss includes 
a very great number of different kinds of invertebrates. 




A centipede (above). A millipede (below). 
Why are both of these animals classified as arthropods ? How do they differ ? 

Some of them with which you are familiar are grasshoppers 
and flies, lobsters, crayfishes and crabs, spiders and centi- 
pedes. Is there not some striking characteristic which 
you have already observed in some of these animals which 
will enable you to see why biologists classify them and 
thousands of similar animals in the same branch of the 
animal kingdom ? You will surely have observed that some 
of the animals named above have jointed legs, and that 
such forms as the lobster (111. p. 528), crayfish (111. p. 526), 



ANIMAL CLASSIFICATION 



383 



and crabs have bodies that are partly, at least, covered by 
a series of rings of a hard, protecting material. All an- 
imals that have jointed legs and an external skeleton which 
is divided more or less into a series of rings are called arthro- 
pods (ar'thro-podz). The scientific name for this branch of 
the animal king- 
dom is Arthrop- 
oda (ar-throp'- 
6-dd, from the 
Greek, meaning 
jointed feet) . In 
your study of 
Unit 9, problems 
6 and 7, you will 
have an oppor- 
tunity to become 
better acquainted 
with a few out of 
the hundreds of 
thousands of 
kinds of arthro- 
pods. You will 
then be better 
able to under- 
stand why biolo- 
gists have divided the arthropods into smaller groups, called 
Classes. All the arthropods we shall study may be classified 
in one or the other of two classes. These Classes are the In- 
sects and Crustaceans (krus-ta'shanz) . The grasshoppers and 
flies are insects and the crayfishes and lobsters are crustaceans. 
Annelids. Doubtless you have all seen the earthworm (111. 
p. 532), so commonly used for fish bait. The earthworm, the 
sandworm (111. p. 534), and the leech (111. p. 534) have bodies 




From Walter's "Vertebrate Zoology 

The devil-fish (Octopus) (a mollusk) 
It swims by forcing water out between the long arms and 
thus drags the arms behind it. The suckers on the arms 
enable it to hold on to its prey. 



384 



ANIMALS AND HUMAN WELFARE 




composed of a series of rings, but no jointed legs. Therefore 
they cannot be classed with the arthropods. The name that 
has been given to this branch of the animal kingdom is Annel- 
ida (d-nel'i-dd,from the Latin anellus, meaning a little ring). 
Mollusks. A fourth branch of the animal kingdom may- 
be represented by clams, oysters, snails (111. p. 537), and 
the octopus (111. p. 383). None of these animals has either 

jointed legs or bodies com- 
posed of rings. Their bodies 
are always soft, and usually 
protected by a shell, and 
so are popularly called shell- 
fish. The branch to which 
all these animals belong is 
called Mollusca (mo-hls'kd, 
from the Latin mollusca, 
meaning a soft nut with a 
thin shell). 

Coelenterates. You have heard of jellyfish (111. above), 
corals (111. p. 540), and the sea anemone even if you have 
not seen them except in pictures. These invertebrates have 
neither jointed legs nor a body made up of rings. Neither 
have they a digestive tract separate from the body cavity as 
have the animals in the preceding branches. Such animals 
constitute a fifth branch of the animal kingdom, Coelenterata 
(se-len'ter-a'td, from the Greek, meaning hollow intestine). 

Porifera. Every one is familiar with the common bath 
sponge (111. p. 541). The bath sponge as we know it is only 
the framework to which the living cells were attached. 
The holes (pores) that you have seen in a sponge lead into 
channels that reach all parts of the sponge. On account 
of these pores, the sponges are given the name Porifera 
(po-rif'er-d, from the Latin, meaning pore bearing). 



A jellyfish 
The mouth is at the lower end of the projec- 
tion inside the "bell." 



MAMMALS AND HUMAN WELFARE 385 

Protozoans. The seventh branch of the animal kingdom 
includes the simplest forms of animals, since they have only 
one cell. On pages 209-211 we studied the reproduction of 
one of these one-celled animals, the amoeba (111. p. 211). 
All one-celled animals are called Protozoa (pro'to-zo'd, 
from the Greek, meaning first animal). 

Thus we see that the animals in each of the seven branches 
we have discussed are related because of one or more com- 
mon characteristics of structure. We shall now proceed to 
study a few animals from each of the classes of vertebrates 
beginning with the mammals. 

QUESTIONS AND APPLICATIONS 

1. Show why environment cannot be used as a scientific basis for classi- 
fying animals. 

2. Name several branches of the animal kingdom and show how these 
groups differ from each other. 

3. What is the basis for the scientific classification of animals? 

4. Supply the necessary words to complete the meaning in the follow- 
ing : If you find that an animal you are studying has a bony skeleton, 
it belongs to the branch of the animal kingdom known as (a). If the 
body of the animal is made up of a series of rings and jointed appendages 
are present, the animal belongs to the (b) branch. If no jointed append- 
ages are present but the body is composed of a series of rings, the animal 
belongs to the branch (c). The Coelenterates have no (d) separate from 
the body cavity. The Protozoa consist of only (e). Clams, oysters, and 
snails belong to the branch (/) . The invertebrates include all the animals 
that have no (g). 

PROBLEM 2. HOW ARE MAMMALS RELATED TO HUMAN 

WELFARE ? 

Characteristics of mammals. One would hardly suppose 
that animals as different as the ocean-dwelling whale 
(111. p. 14), the flying bat, the enormous elephant (111. p. 386), 
the tiny mouse, and the domestic horse (111. p. 253) could all 



386 



ANIMALS AND HUMAN WELFARE 



be included in a single class. Yet such is the case. Mam- 
mals usually have a skin that is more or less hairy. In a 
few cases, however, no hair is present, e.g. the armadillo. 
The texture and density of this hairy coat, however, vary 
greatly among mammals. On the whale the hairs are as few 




_, , , Courtesy of New York Zoological Society 

The elephant 
The two tusks are greatly developed incisor teeth. 

and as far between as they are on the shining heads of 
some of our human acquaintances. On the Northern musk 
ox (111. p. 387) the shaggy covering is so long that it 
almost reaches to the ground. Furthermore, the amount 
of hair on some mammals varies greatly at different times 
of the year. Those of us who are familiar with the horse 



MAMMALS AND HUMAN WELFARE 387 



know that at certain seasons the hair falls out and a new 
coat appears. 

Again, all the animals named above, and many others, 
develop their young within the body and feed their young 
for a time after birth on milk which is secreted in mammary 
glands. Because of the possession of these glands the ani- 
mals of this class are 
known as mammals. 
This method of feed- 
ing their young is, of 
course, familiar to 
us in the case of the 
cow, dog, and other 
domesticated ani- 
mals; but it may 
not be so well known 
that seals, whales, 
and porpoises like- 
wise feed their 
young on milk. Fe- 
male opossums and 
kangaroos, after the young are born, put them into pouches 
on the lower front part of their body (111. p. 388) . The pouch 
serves not only as a means of protection, but also as a place 
for feeding the offspring, since within it are the mammary 
glands that secrete the milk needed by the young. A still 
more unfamiliar mammal, which like the kangaroo inhabits 
Australia, is the duckbill (111. p. 389). Although this animal 
is covered with hair and secretes milk for its young, it re- 
sembles the birds in that it lays eggs from which the young 
are produced. 

A third distinguishing characteristic of the mammals is 
the presence of a complete diaphragm (111. pp. 94, 117), which 




Courtesy of New York Zoological Society 

The musk ox 

Find out how these animals of the Arctic region secure 

their food 



388 



ANIMALS AND HUMAN WELFARE 



separates the chest cavity from the abdominal cavity. 
This structure is absent in all other animals. Most mam- 
mals, too, have a body temperature about like that of man, 
whether, like the polar bears (111. p. 397) and Arctic foxes, 
they live in the frozen regions of the Far North or, like the 




Courtesy of New York Zo'dlogical Society 



The kangaroo 
How is the young kangaroo protected and nourished ? 

tigers and elephants (111. p. 386), they inhabit the tropical 
jungles. 

We may say, therefore, that a mammal is a warm-blooded 
vertebrate that feeds its young on milk and that has a hairy 
covering and a diaphragm. Most of the mammals have a 
distinct head, neck, trunk, and tail and two pairs of ap- 
pendages. In man, however, and in manlike apes the tail 
is undeveloped. Mammals are found in all parts of the 






MAMMALS AND HUMAN WELFARE 389 



world, with the possible exception of some of the islands of 
the Pacific Ocean. 

Mammals as beasts of burden. Man has made large 
use of mammals as beasts of burden. The most familiar 
type is the horse. This animal and its near relatives, the 
donkey and mule, have been used for thousands of years. 
By careful selection and breeding such different types of 
horses have been developed as the small Shetland pony, 




A native of Australia. 



Courtesy of American Museum of Natural History 

The duckbill 
How does it resemble and how does it differ from a bird? 



the draft horses used for hauling heavy loads, and the trot- 
ting and racing breeds that have made astonishing records 
for speed (111. p. 253). Among the wild relatives of the 
horse is the zebra. 

The camel with its cushionlike feet is particularly fitted 
for carrying burdens across sandy regions. For this reason 
the camel has frequently been referred to as the " ship of 
the desert." As such it has played an important part in 
the history of the Old World, especially among the nations 
of the East. Not only is the camel adapted by the shape 



390 



ANIMALS AND HUMAN WELFARE 



of its feet for desert travel, but also by its stomach which 
has a large number of pockets (water cells) that will hold 
enough water to last the animal for days. 

As the camel is the beast of burden of the tropical deserts, 
so the reindeer (111. below) may be regarded as specially 
fitted to provide means of transportation in the Arctic 
regions. These animals have wonderful ability to thrive 



NH0H 


IBM 




:*''' 


1 1 % K 

4 1 ■ , \ ; ■.... 1; 





Courtesy of United States Biological Survey 

A herd of reindeer 
What are two uses of these animals of the Arctic regions ? 

on the poor food furnished by Arctic plants and to endure 
extremes of cold. Eskimo dogs, too, are of great value, 
being used in hauling sledges. These two animals fulfill all 
needed requirements of those northern dwellers who depend 
so much on their aid. 

Mammals as sources of food. Most kinds of mammals, 
with the exception of some members of the cat and weasel 
families, are used as food by some of the races of the earth, 
and this is perhaps their most important relation to human 



MAMMALS AND HUMAN WELFARE 



391 



welfare. The hoofed animals are of prime importance since 
to this group belong cattle, sheep, and pigs. Consider first 
the importance of the millions of cows in our country in the 
production of milk, from which butter and cheese are also 
made. So far has biology been applied to human welfare 





■...'"' — . '*-yr 


*%r 




mMf' * * ^wfti 


^^ .'"- L^j| 


ta 




Vf'ii 


*Ojtf 


f -BBFfi^^r^H|yr iw ' jf. 




• *f '• ikJ^V ^K 




Mi 

■ mill 


Lf ( | 


i^^ 


•* 
1 1 


■nflflnf v v * - • 



A herd of seals 



Courtesy of U. S. Bureau of Fisheries 



These mammals are found in large numbers on the Pribilof Islands off the coast of 

Alaska. 

in the dairy industry that the modern farmer is able to breed 
cattle especially fitted to produce milk either especially 
rich in butter fat or great in quantity. So highly developed 
has become the modern slaughtering and packing industry 
that practically every part of the animal is utilized. 
The seal (111. above), walrus, caribou, and musk ox (111. 
p. 387) are valued as food in the Arctic regions and especially 



392 ANIMALS AND HUMAN WELFARE 



for the supplies of needed fats which these animals furnish. 
And in recent years reindeer have been raised for their 
meat which is shipped even to the United States. 

Mammals as sources of clothing. Next in importance 
to the food furnished to man by mammals, we may name 
the value of this group of animals as a source of clothing. 

Off the coast of Alaska are 
the Pribilof Islands, the 
breeding place of the Alaska 
fur seals (111. p. 391). This 
animal, most valuable as a 
source of fur, was in grave 
danger of extinction before 
the United States Govern- 
ment succeeded in enforcing 
prohibition .of open-ocean 
killing. 1 The American 
bison (commonly called the 
buffalo) is now found only 
in protected areas. These 
animals, in the early history 
of our country, roamed the 
Western plains in countless 
numbers, and their hides 
were of great value because 
of their dense curly hair. 
The list of fur-bearing mammals of value to man is a 
long one. It includes, among others, the muskrat, bear, 
opossum, mink, otter, beaver, skunk (111. above), mole, 
squirrel, raccoon, fox, and seal. Some of these (e.g. foxes 
and skunks) are bred in captivity. It is becoming a grave 
question, however, whether the enormous demand of women 

1 For an account of seal slaughter, see Jack London's novel Sea Wolf. 




Courtesy of U. S. Biological Survey 

The skunk 
A fur-bearing mammal. What is the com- 
mercial name for skunk fur ? 



MAMMALS AND HUMAN WELFARE 393 

for the furs of wild animals, not only for winter warmth but 
also for summer adornment, will not bring about the early 
extinction of some species, unless constructive management 
practices are adopted. 

Mammals as sources of other valuable commercial 
products. Besides their value to man as a means of trans- 
portation and as a source of food and clothing, mammals 
furnish us with valuable commercial products. From the 
tusks of elephants (111. p. 386) and walruses comes the 
precious ivory. Hoofs, horns, blood, and bones are used in 
the manufacture of buttons, ornaments, handles, glue, and 
gelatin. Bone black is used in refining sugar. The fine 
hair of camels is largely employed for soft paint brushes, 
and the coarser bristles of pigs, badgers, and other animals 
are made into brushes for other uses. 

Blood and parts of animals not used for other purposes 
are sold by the packing houses for the manufacture of ferti- 
lizer. In former days, before the discovery of petroleum 
and before electric lighting was thought of, the whaling in- 
dustry was of immense importance. From the whales were 
extracted great quantities of oil, most useful in those early 
days for illumination. 

Rodents harmful to field crops. There are about 1350 
different kinds of rodents in North America. The muskrat 
and beaver (111. p. 394) are valuable for their furs, but a few 
of these gnawing animals are injurious to crops. Some of 
them, like the field mouse, kangaroo rat, pocket gopher, 
ground squirrel, and prairie dog (111. p. 394), cause such 
enormous damage to field crops that they must be controlled 
over large areas by cooperative action of the farmers and 
stockmen, or the regions which they infest must be aban- 
doned. The Biological Survey in Washington states that 
these harmful rodents, including the house rats and mice, 



394 



ANIMALS AND HUMAN WELFARE 



have caused an annual damage of $500,000,000 to our crops 
and other property. Fortunately, however, the National 
Government has made a study of the life habits of each of 




Prairie dog 




Beaver 




Mouse 





Squirrel 




Jumping jerboa 



From Waller's "Vertebrate Zoology" 

Various types of gnawing animals (rodents) 
The incisor teeth of rodents are specially developed. How do they get their food ? 

these species, and has devised effective methods of control- 
ling the pests. It has been found that if poisoned baits are 
properly prepared and then carefully placed in small quanti- 



MAMMALS AND HUMAN WELFARE 395 

ties in the infested areas, these areas can be very largely 
rid of the rodents. Care must be taken in this work that 
the poisoned bait be so placed that it will not be eaten by 
birds or grazing animals. 1 

Rodents harmful to stored food and to health. House 
rats and mice are a serious source of property loss and of 
danger to health if allowed to live in or about the habitations 
of man. " The rat is the most destructive animal in the 
world," wrote Professor D. E. Lantz of the U. S. Depart- 
ment of Agriculture. This authority estimated that in the 
United States alone rats destroy each year $200,000,000 
worth of property. Let us see how this is possible. In the 
first place, where food is plentiful, rats may breed six to 
ten times a year and may average ten young in each litter. 
These animals feed and reproduce in the open fields in 
summer ; in winter they seek shelter in barns and store- 
houses. Hence they are exceedingly destructive to standing 
grain or to grain that is stored and to food for man in 
storehouses and homes. 

But the worst indictment brought against these pests is 
the fact that rats are an agency for carrying disease germs. 
The terrible bubonic (bu-bon'ik) plague is a disease that 
results from germs carried to human beings by fleas that 
infest rats and certain ground squirrels. Rats are subject 
to the bubonic plague and when the rats die from the disease, 
the fleas from their bodies infest other hosts that may be 
near, such as human beings. The fleas suck the blood of the 
human host and in so doing introduce the germs which 
they have obtained from the blood of the rats. Hence it 
is always a filth disease that is preventable. The black 
death of the fourteenth century which swept over Europe 

1 See "Death to the Rodents" by W. B. Bell, Bureau of Biological Survey, 
Washington, D. C. 



396 



ANIMALS AND HUMAN WELFARE 



and killed 25,000,000 people was an epidemic of bubonic 
plague. One of the latest outbreaks of the disease was in 
one of the large American cities. As a result, however, of 
the application of known biologic principles only a relatively 
few deaths occurred before the disease was stamped out by 





American buffalo 




Giraffe 



Camel 



Moose 

From Walter's "Vertebrate Zoology" 

Various types of hoofed-animals (ungulates) 
Molar teeth are especially developed in all these animals. What kind of food do they 

eat? 

local control efforts, including destruction of rats and ground 
squirrels. 

It is evident, therefore, that the individual and the 
public should take every possible means to starve the rats 
during the winter by careful storing of foods, and to catch 
as many as possible of them by means of traps. House 
mice and field mice likewise are destructive and they should 
be effectively controlled. 1 



See "Rat Control," Farmers' Bulletin 1533, by James Silver, Washington, 



D.C. 



MAMMALS AND HUMAN WELFARE 397 



The classification of mammals. Rodents. The mammals 
are divided into groups known as orders. Thus the mammals 
that have sharp incisors and molars, but no canine teeth, 
are called the gnawing mammals. Examples are the rats, 
mice, squirrels, beavers, rabbits, woodchucks. All these 
mammals are placed in the order, Rodentia (ro-den'shi-d, 
from the Latin, meaning gnawing) (111. p. 394). 




Wolf 



Red fox 



Coyote 

From Walter's "Vertebrate Zoology" 

Various types of carnivora 
The canine teeth are especially developed in the carnivora. What kind of food do they 

eat? 

Ungulates. In horses, cows, sheep, deer, and other 
herbivorous mammals the molars are especially well devel- 
oped while the canine teeth are wanting or are relatively 
small. The nails on the toes of these mammals are devel- 
oped into what are known as hoofs. In the horse each foot 
has only one hoof, the cow two, and the elephant five. All the 
mammals that have hoofs are grouped in the order, Ungu- 
lata (tin 'gu-la'td, from the Latin, meaning hoof) (111. p. 396). 

Carnivora. Dogs, cats, lions, and tigers have sharp 
pointed incisors and long canine teeth for tearing their food. 



398 ANIMALS AND HUMAN WELFARE 

Since all these mammals live mainly on other animals 
which they catch and kill, they are classed in the order, 
Carnivora (kar-niv'6-rd, from the Latin, meaning flesh 
eating) (111. p. 397). 

Primates. There remains one other order of mammals 
of which we should speak ; namely, the highest, that to which 




_, .,, Courtesy of New York Zoological Society 

The gorilla 
This largest and fiercest of the apes inhabits a small area of the tropical forests of 

West Africa. 

man belongs. This group also includes the monkey, the 
baboon, and the ape. To the latter group belong the 
orang-outang (o-rang'oo-tan'), the chimpanzee (chim- 
pan'ze), and the gorilla (111. above). Because these animals 
excel the rest of the animal kingdom in brain development 
and in intelligence, this order of mammals is known as the 
Primates (from the Latin, meaning first). Some of these 
animals, " while resembling the human species in many 
characteristics, must of course be recognized as having 



MAMMALS AND HUMAN WELFARE 399 

evolved (developed) along special lines of their own, and none 
of them are to be thought of as the source or origin of the 
human species. It is futile, therefore, to look for the primi- 
tive stock of the human species in any existing animal." x 

QUESTIONS AND APPLICATIONS 

1. Give three or four characteristics that distinguish mammals from 
all other animals. 

2. What is the largest living mammal? The smallest? 

3. Name two distinctive mammals of Australia and show how they 
resemble and how they differ from other mammals. 

4. Name as many mammals as you can that spend all or a considerable 
part of their lives (a) in trees, (6) beneath the ground, (c) in the water, 
(d) in Arctic regions, (e) in the deserts. What characteristics of structure 
adapt each of them for its methods of life ? 

5. Name six different kinds of mammals used by man for transportation 
and show some of the ways each is adapted for the kind of work it does. 

6. Name six kinds of mammals used by man for food, stating the kind of 
food supplied by each. 

7. Enumerate ten mammals that supply material for clothing or adorn- 
ment, stating the kind of material supplied by each. 

8. Name several useful mammals in danger of extermination and sug- 
gest ways of preventing this. 

9. Show numerous ways in which rats and mice cause enormous injuries 
to man. Suggest ways of holding these mammals in check. 

10. Name five or more other mammals that are injurious to man, stat- 
ing how each is injurious. 

11. What animals belong to the order of mammals known as Primates? 
Why are they so called ? 

12. Which mammals secure or kill their prey (a) by creeping upon 
them, (b) by tearing them with teeth or claws, (c) by swimming through 
the water? 

13. Complete the following sentences : (1) Camels are adapted for long 
journeys over the sands of deserts by their (a) and (6). (2) Reindeer are 
very useful animals in the Arctic regions because they serve as (a) and 
as (6). 

1 From Osborn, Herbert, Economic Zoology. Used by permission of The Mac- 
millan Company, publishers. 






400 ANIMALS AND HUMAN WELFARE 

14. Which mammals have the following teeth especially developed 
(a) incisors, (6) cuspids, (c) premolars and molars? State the kind of 
food eaten by each of the animals you have named. 

15. Study the claws of a cat and of a dog. What striking difference do 
you find? 

16. Which mammals have become a special menace to man because of 
their rapid reproduction? 

17. In what ways is man superior to all other members of the animal 
kingdom? Name animals that have a keener sense of smell ; more rapid 
locomotion. 



PROBLEM 3. HOW ARE BIRDS RELATED TO HUMAN 

WELFARE ? 

Some questions one may ask about birds. Have you 

ever thought what would happen to the human race if all 
birds were to disappear? Would you say that birds are 
increasing or decreasing in numbers in this part of the coun- 
try? Do you think it would be possible to get a scientific 
answer to this question? Are you sure you could distin- 
guish a bird from all other kinds of animals? This, you 
would find, is not quite so easy as would appear at first sight. 
Can you explain why birds should interest all of us? Can 
you tell in what ways birds are most useful to man? Do 
you know any birds that are harmful to man? In what 
respects, if any, do the flying machines invented by man 
resemble birds in the method of flying? Have you any 
idea how scientists are able to determine the kinds of food 
and the amount eaten during a year by robins, crows, or 
other kinds of birds? What do you know from personal 
observation about the family life of birds ? The pages that 
follow should give you answers to most of these questions. 
How birds differ from other animals. If you were asked 
to give the most striking characteristic of birds, you would 
perhaps say that it is their ability to fly. True it is that 



BIRDS AND HUMAN WELFARE 



401 



nearly all birds possess this power in a greater or less degree ; 
but so do butterflies, bees, and other insects. Have you 
not also heard of bats, flying fishes, and flying squirrels? 
You would not, of course, think of these as birds, even though 
they do possess to 
some extent the 
power of moving 
through the air. 

If you have ever 
held in your hands a 
living bird, were you 
not surprised to find 
it so warm? The 
temperature of some 
of the sparrows and 
warblers is 12° higher 
than that of man. 
While this high tem- 
perature is charac- 
teristic of most birds, 
there are some with 
a degree of heat con- 
siderably below 
98.6°. 

If, then, neither 
the possession of wings nor a high temperature is the dis- 
tinguishing characteristic of this group of animals, is there 
any way in which every bird is different from every other 
living thing? We find our answer in the facts that every 
bird has a covering of feathers and that feathers never develop on 
any other animal. Fishes, we know, have a characteristic 
outer layer of scales, and this is also true of reptiles (snakes, 
lizards, and alligators). The highest group of animals, on 




Photograph by Elwin R. Sanborn 

Different types of feathers 
Left to right : wing feather, tail feather, downy feather. 






402 



ANIMALS AND HUMAN WELFARE 



the other hand, the group to which the dog, horse, and man 
belong, has a body covering of hair. 

The head of the bird and its organs. Even a casual exam- 
ination of a bird (111. below) shows us that it has a head, 
neck, and trunk, and two pairs of limbs ; namely, the wings 
and the legs. A more careful study shows that from the front 



*.-- Crown 



Nape 

^-Back 

^-Lesser wing coverts 




Greater coverts 
— Rump 

-Secondaries 
— Primaries 



— Tail 



From Traf tori's ' ' Biology of Home and Community 

Regions of a bird 



part of the head projects- a horny structure known as the 
beak, or bill. " Tie a man's hands and arms tightly behind 
his back, stand him on his feet, and tell him that he must 
hereafter find and prepare his food, build his house, defend 
himself from his enemies, and perform all the business of 
life in such a position, and what a pitiable object he would 
present ! Yet this is not unlike what birds have to do. 









BIRDS AND HUMAN WELFARE 



403 



Almost every form of vegetable and animal life is used as 
food by one or another of the species. Birds have most 
intricately built homes, and their methods of defense are to 
be numbered by the score ; the care of their delicate plum- 
age alone would seem to necessitate many and varied in- 
struments ; yet all this is made possible, and chiefly executed, 
by one small portion of the 
bird — its beak or bill." * 

Near the base of the bill, 
on either side, one can usu- 
ally see an opening; these 
openings are the nostrils 
(111. p. 402). On the sides 
of the head are the two 
eyes, which bulge out some- 
what. As an example of 
keenness of vision in birds, 
we may cite the following 
incident : A kingbird (111. 
at right) was seen by Dr. 
Oberholser of the United 
States Biological Survey to 
start from a telegraph pole, 
to fly swiftly in a direct 
line, and to capture an insect so small as to be invisible to 
the human eye only twenty-five feet away. By actual 
measurement the distance from which this bird espied its 
victim was 150 feet. This shows an ability to distinguish 
objects more than six times that possessed by a human 
being. If the feathers below and behind the eye are pushed 
aside, an opening into the ear may be seen ; this may be 




Courtesy of U. S. Bureau of Biological Survey 

Kingbird 
Of what does its food mainly consist ? 



1 From Beebe's The Bird. Used by permission of Henry Holt and Company, 
publishers. 



404 ANIMALS AND HUMAN WELFARE 



made out easily in the head of a fowl. External ears are 
absent in all birds. 

While the size and shape of the bill vary greatly in differ- 
ent kinds of birds, the bill always consists of two parts 

(mandibles) (111. p. 402), 
which correspond in posi- 
tion to the upper and 
lower jaws of man. 
When the bill is opened, 
a careful examination 
shows that a bird has no 
teeth. Some of the birds 
that lived ages ago, how- 
ever, had well-developed 
teeth in their jaws, as 
is shown in the illustra- 
tion on this page, which 
is a picture of a bird 
skeleton restored from 
bones found in the clay 
deposits of western 
Kansas. 

Adaptations of birds 
for flight. The illustra- 
tion on page 405 shows 
the bones that compose 
the wing of an ostrich 
and the arm of a man. 
On comparing the two, one sees a striking resemblance. In 
both, the upper arm has a single bone, while the forearm 
has two. In the hand region, though the differences are 
more striking, the general plan of the two is the same. The 
wings of all birds are constructed on the same general plan 




Courtesy of American Museum of Natural History 

Reconstruction of a fossil bird 
Note the teeth that are never found in present- 
day birds. The bones that are represented in 
black are those actually found in the rocks ; those 
in white have been supplied by plaster casts. 



BIRDS AND HUMAN WELFARE 



405 



as that of the ostrich. Unlike the bones of the human 
skeleton, those of the wings and legs of most birds are hol- 
low and filled with air ; hence a bird's skeleton is relatively 
very light in weight. The flesh on a bird's wing is composed 
largely of ?nuscles 
that enable the ani- 
mal to fold and un- 
fold the parts of the 
wing, as the human 
arm is doubled up 
or stretched out (111. 
at right). On the 
bird's body are other 
powerful muscles 
that cause the wing 
as a whole to make 
the downward and 
upward strokes in 
flight. When the 
bird makes the 
downward stroke, 
the wings are ex- 
tended so as to strike 
against the largest 
possible surface of 
air. In the upward 
stroke the wings are 
folded back at the elbow ; and so, when raised edgewise, 
their smaller surface presents little resistance to the air (111. 
p. 403). 

Thus we see that the forward-propelling power of a bird 
largely results from the movements of the wings. In an 
airplane, on the contrary, the wings are constantly outspread 




Photograph by A. E. Rueff 

Skeletons of anterior appendages 
A, Human arm; B, Wing of ostrich. 



406 ANIMALS AND HUMAN WELFARE 

and to a large extent are fixed in their position, and the 
machine is driven by a rapidly revolving propeller out in 
front of the machine. The bird steers its course by varying 
the position of its tail feathers. The same principle is 
applied in the movement of the rudder of an airplane. 

Adaptations of the legs and feet of birds for their functions. 
By comparing the arm of a man with the wing of a bird, 

we found that they 
were similar in gen- 
eral structure in 
spite of their striking 
differences in func- 
tion. Is the same 
likewise true of the 
leg and foot of man 
and of a bird? While 
the thigh of a bird 
is much shorter pro- 
portionately than 
that of a man (111. 
p. 407), in each there 
is but a single bone. Below the knee of the bird is the 
shank, or drumstick, which consists of a long bone extending 
to the ankle, and beside it is a thin bone attached only at 
the upper end. This region in the leg of a man is likewise 
composed of a relatively thick shin bone, on the outer side 
of which is a slender bone extending down to the ankle. 
The ankle region of the bird is the joint halfway up the leg 
(111. p. 407). What is commonly regarded as the bird's foot 
consists of four, three, or two toes that point forward and 
often one or two that extend backward. Ordinarily the 
parts of the leg below the ankle are covered with scales, 
and the tips of the toes are provided with nails, or claws. 




Courtesy of Science Service 



The gull 

How does the position of wing feathers, tail feathers, 
and of feet adapt the bird for rapid flight ? 






BIRDS AND HUMAN WELFARE 



407 



Wings, we have found, are organs specially adapted for 
flight. Are the legs of a bird likewise limited to a single 
function? Watch any common song bird (e.g. a canary, 
robin, or sparrow), and you will see that, when it alights on 
a branch, it clings to 
this support by clasp- 
ing it tightly with its 
three front toes and 
a single hind toe (111. 
p. 418). 

The legs and feet 
of all birds are also 
used for locomotion. 
Many of the smaller 
birds move from 
place to place by 
hopping, others by 
walking, while still 
other birds (e.g. fowls 
and ostriches) can 
run with considerable 
speed. Birds like the 
herons, which wade 
out into the water in 
order to secure their 
food, are adapted for 
this purpose by hav- 
ing remarkably long legs. And finally ducks and swans 
secure locomotion in the water by means of their webbed 
feet. 

The legs of birds are adapted not only for perching and 
locomotion but also for use in many cases for securing food. 
This is notably true of eagles (111. p. 408), hawks, and owls 




Photograph by A. E. Rueff 

Skeletons of posterior appendages 
A, Leg of ostrich ; B, human leg. 



408 



ANIMALS AND HUMAN WELFARE 



(111. p. 409), which possess long, sharp, incurving claws, or 
talons, by which they clutch and carry off their prey. Other 
birds, such as domestic fowls, have strong nails with which 
they scratch the ground and thus uncover the insects and 
vegetable foods which they eat. Most of the members of 
the woodpecker family have two toes in front and two 
behind, each provided with sharp claws (111. p. 410). By 

the help of these 
claws they can cling 
to the trunks or 
branches of trees 
and so be in a posi- 
tion to secure their 
insect food with 
their barbed tongues 
after chiseling holes 
with their long, 
sharp bills. 

Reproduction of 
birds. Fish eggs, we 
have learned, need 
no parental care to 
insure their hatch- 
ing, for the process goes on when the water is of the right 
temperature and when other favorable conditions are present. 
The same is true of the eggs of many other animals ; for ex- 
ample, insects, frogs, turtles, and snakes. Birds' eggs, on the 
other hand, require a degree of warmth that is considerably 
higher than the ordinary temperature of water and air. 
This temperature is secured naturally when the parent bird 
broods over the eggs. In the case of the domestic fowl about 
three weeks are necessary for the development of the fertilized 
egg cell into a chick (111. p. 411). When the process is com- 




From painting by John J. Audubon 

The eagle 

How are the claws and the bill of this bird adapted for 

securing animal prey ? 



BIRDS AND HUMAN WELFARE 



409 



pleted, the young bird pecks its way out of the shell and is then 
ready to secure its own food under the direction of its mother. 

Structure of a hen's egg. The outside of the hen's egg is 
a rather thin, brittle shell, which is lined with a thin, white 
membrane. A second mem- 
brane incloses the liquid por- 
tion, or the white of the egg, 
and in the center is the 
yellowi/oZA;(IlLp.411). On 
the surface of the yolk of a 
fresh-laid egg is a tiny circu- 
lar white spot, which can be 
seen if the shell and the 
membranes are carefully cut 
away. This circular spot is 
the beginning of a chick, 
and it is the only living 
part of the egg. The yolk 
and white of the egg consist 
of food materials stored up 
by the mother for use in 
the development of the baby 
chick. Let us now see how 
these various parts of the 
egg are produced. 

Formation of a hen's egg. If we examine the internal 
organs of a laying hen, we find a mass of spherical objects, 
varying in size from tiny white dots to full-sized yolks 
that are yellow in color. The yolks and the white dots 
are eggs in various stages of development in the ovary of 
the hen. If any one of the yolks is examined carefully 
with a compound microscope, a single cell will be found on 
its outer surface. When a yolk is full-sized, it is released 




Courtesy of U. S. Bureau of Biological Survey 

The great horned owl 
Compare the beak and talons of this bird 
with those of the eagle (111. p. 408). What 
has the bird caught in its talons ? 






410 



ANIMALS AND HUMAN WELFARE 



from the ovary and enters the open end of the spirally- 
twisted egg tube. As the yolk passes down this tube on its 

way to the exterior, special 
cells lining the tube pour 
out upon it the translucent 
white, or albumen. Farther 
down the tube other cells 
form the two inclosing mem- 
branes (111. p. 411). And, 
finally, the hard shell is se- 
creted before the egg is laid, 
although at times soft- 
shelled eggs (i.e. those with- 
out a shell) are deposited. 

Fertilization in a hen's 
egg. Just as we found that 
a fish egg does not develop 
into a young fish unless it 
has been fertilized by the 
nucleus of a sperm cell, so, 
too, the egg cell of a bird 
must be stimulated by this 
process of fertilization. 
Would it be possible for this 
process to take place outside 
the body of the hen after 
the egg is laid, as is the case 
with the fishes ? Evidently 
not, since the sperm cells 
would be unable to penetrate the shell, the membranes, and 
the white of the egg, before reaching the egg cell on the yolk. 
Therefore the sperm cell must reach the yolk in the upper 
part of the egg tube before the rest of the egg is formed. 




Courtesy of U. S. Bureau of Biological Survey 

The woodpecker 
Note the two front and the two hind 
toes, the stiff tail feathers, and the strong, 
pointed bill which it uses for drilling the 
holes in search of food. 






BIRDS AND HUMAN WELFARE 



4U 



When a sperm cell reaches and penetrates the egg cell, 
and when the sperm nucleus fuses with the egg nucleus, the 
egg cell becomes fertilized. It now divides and subdivides, 



Wnk 


^v 


f rllT^B* 


S lit jit -•«- *-jfe » 




5 Days ifl 


Hi 'ODays jK' 


PH K^i 


■j 15 Days i|H| 



Courtesy of American Museum of Natural History 

Development of a chicken 
At the left (larger) end of the egg is the air space for the embryo. Note the blood 
vessels through which the embryo secures its food, first from the yolk of the egg and 
later from the white. 

as it passes down the egg tube, until a many-celled stage is 
reached at the time the egg is laid, and then it is sufficiently 
large to be seen with the naked eye. Further development 
into the chick can- 

Young embryo 



/Shell 

^Outer shell membrane 
—-Inner shell membrane 

--Air space 

— Chalaza 
—Yolk 

Membrane 

— enclosing 
yolk 

Structure of a hen's egg 

Locate the white of the egg. What part of this egg 

is alive ? Name all the lif eless parts. 




not take place unless 
the egg is kept warm 
either by the mother 
hen or in an incu- 
bator. When these 
favorable conditions 
are present, cell di- 
vision continues, and 
the cells become dif- 
ferent in character. 

Gradually the various regions and organs of the bird are 
formed (111. above), and the chick hatches, that is, it emerges 
from the shell (111. p. 412). 



412 ANIMALS AND HUMAN WELFARE 

Care of birds for their young. In contrast to most of the 
animals we have named on page 408, most birds show 
a high degree of care for their young, usually building 
nests to receive the eggs. The number of eggs that are laid 
is relatively small. Chickens and quail on hatching from 
the egg are able to run about and pick up their food under 



Newly hatched chicken 
Would a robin just hatched be able to stand ? 

the protection and with the help of the mother bird. Many 
birds on hatching from the egg, for example, robins and spar- 
rows, are much more helpless than are chickens, and so the 
food is brought to the young in the nest by the parents. 
Indeed some parent birds partially digest the food before 
the young receive it. Parental care and protection from 
enemies is continued until the birds are able to fly and often 
for a longer time. 



BIRDS AND HUMAN WELFARE 



413 



Nests differ greatly in their complexity and. in the kind of 
material used. Birds such as some of the gulls and many 
other sea birds usually deposit their eggs on rocky ledges 
or in slight depressions in the sand along the shore. On the 
other hand, the Baltimore oriole constructs out of grasses, 
plant fibers, and strings a marvelous nest often high up in 
the trees near the outer 
ends of the branches. Be- 
tween these two extremes 
are all gradations of nest 
complexity (111. p. 414). 

The eggs laid by birds 
vary also in number, size, 
and color. For example, 
the tiny humming bird lays 
two white eggs about the 
size of a small bean ; the 
robin lays three to five 
bluish eggs, each nearly an 
inch in length, and the ostrich usually lays twelve to twenty 
eggs, each weighing three to four pounds (111. p. 415). The 
incubation period in the case of birds varies from ten days 
(song sparrow) to forty-two days (ostrich). 

Migration of birds. " For more than 2000 years," says 
a Government Bulletin, 1 " the phenomena of bird migration 
have been noted ; but while the extent and course of the 
routes traversed have of late become better known, no con- 
clusive answer has been found to the question, Why do 
North American birds migrate? " 

The various theories advanced to account for bird migra- 
tion have to do largely with the necessity of securing proper 





_ '„ ,jefS8 * 







Baltimore oriole, a beautiful songster 
How is this bird useful ? 



1 See "Bird Migration," Bulletin No. 185, United States Department of Agri- 
culture. 



414 



ANIMALS AND HUMAN WELFARE 



places for nesting and for raising the young. The map on 
page 416 gives some idea of the principal routes of travel 
southward and northward. By far the largest number of 
our birds follow Route 4 and strike directly across the 500 

to 700 miles of the Gulf of 
Mexico. One of the longest 
known flights of birds is that 
of the golden plover, which 
leaves its breeding place far 
beyond the tree line above 
the Arctic Circle, crosses to 
Nova Scotia, and thence 
launches itself over the At- 
lantic for its long aerial jour- 
ney of 2400 miles by Route 1 
to the coast of South Amer- 
ica. After a six months' 
vacation from family cares 
in Argentina, it returns 
across the Gulf of Mexico 
and thence up the Missis- 
sippi Valley to its nesting 
grounds in the barrens of the 
Arctic. Thus it completes 
a round trip of over 16,000 
miles ! 

Some of the birds, like the chickadee and downy wood- 
pecker, remain in the middle and northern United States 
throughout the whole year and hence are known as permanent 
residents of these regions. Many birds, however, spend the 
winter in the warmer regions (that is, either southern United 
States, Mexico, Central America, or South America) and in 
the spring months move northward. Some of them, like the 




, :k .. J, 

"^ *»:->;: Jr.--: 



Courtesy of Science Service 

Ruffed grouse nest and eggs 
The color and appearance of nest and 
eggs closely resemble those of the sur- 
roundings. 






BIRDS AND HUMAN WELFARE 



415 



catbird and house wren, build their nests, rear their young, 
and stay all summer in northern and middle United States ; 
hence such birds are called summer residents. Still other 
birds rear their young in Canada, and even farther north, 
and come to us in the United States as winter residents. This 
seasonal movement of birds is known as migration. 

Determination of the kinds and amounts of food eaten by 
birds. Few animals are more beautiful in form and color 




Courtesy of New York Zoological Park 

Difference in size of the eggs of birds 

than are many of our most common birds, and one of the 
greatest delights of springtime is to greet the return of the 
bluebirds, tanagers, thrushes, and others of our feathered 
friends. The value of birds as objects of beauty cannot be 
measured, it is true, so easily in dollars and cents. But 
were we to lose the birds, we should realize all too well how 
much they contribute to the happiness of every lover of 
nature. When, however, we come to discuss the purely 



416 ANIMALS AND HUMAN WELFARE 

economic value of birds, the good they do cannot easily be 
overestimated. 

Whether a bird is beneficial or injurious, however, de- 
pends very largely on the kind of food it eats or feeds to 
its young. If the bird devours great quantities of harmful 



Courtesy of U. S. Biological Survey 

Common migration routes of birds 
What is the course that is taken by the largest number of birds? 

insects or of weed seeds, to that extent at least the bird 
is valuable. On the other hand, a bird that feeds largely 
on useful crops, such as fruit or grain, may be considered 
as injurious. 

Biologists have carried on long series of studies to deter- 
mine accurately the food eaten by various kinds of birds. 



BIRDS AND HUMAN WELFARE 



417 



This has been done by watching them while they are eating 
or while they are feeding their young and by examining the 
contents of the stomachs of birds. In this way it has been 
possible to determine fairly accurately the quantities of 
food consumed by a given kind of bird during a season. 
The following paragraphs will show the close connection 
that exists between the nature of the food eaten by birds 
and their usefulness or pos- 
sible harmfulness. 

Usefulness of birds as de- 
stroyers of harmful insects, 
Undoubtedly the greatest 
value of birds to man is the 
good they do in destroying 
injurious insects. In Prob- 
lem 6 of Unit 9 are described 
some of the ravages made 
by our insect foes. Follow- 
ing are statements that will 
give the reader an idea of 
the enormous value of birds 
in reducing the numbers of 
injurious insects : 

" If insects are the natural enemies of vegetation, birds 
are the natural enemies of insects. ... In the air swallows 1 
(111. p. 418) and swifts are coursing rapidly to and fro, ever 
in pursuit of the insects which constitute their sole food. 
When they retire, the nighthawks and whippoor wills will 
take up the chase, catching moths and other nocturnal in- 
sects which would escape the day-flying birds. Flycatchers 




Bluebird 
What has this bird just captured ? 



1 Before this section is assigned for study, each of the birds named, or at least 
their pictures, should be shown to the class. Pictures of the birds may be found in 
Chapman's Bird Life and in leaflets of the National Association of Audubon Societies. 



418 



ANIMALS AND HUMAN WELFARE 



lie in wait, darting from ambush at passing prey and with a 
suggestive click of the bill returning to their posts (111. p. 403). 
The warblers, light, active creatures, flutter about the termi- 
nal foliage and almost with the skill of humming birds pick 

insects from leaf or blos- 
som. The vireos (vir'e-oz) 
patiently explore the under 
side of leaves and odd nooks 
and corners to see that no 
skulker escapes. The wood- 
peckers (111. p. 410), nut- 
hatches, and creepers attend 
to the trunks and limbs, ex- 
amining carefully each inch 
of bark for insects' eggs and 
larvae or excavating for the 
ants and borers they hear 
within. On the ground the 
hunt is continued by the 
thrushes, sparrows, and 
other birds that feed upon 
the innumerable forms of 
terrestrial insects. Few 
places in which insects exist 
are neglected; even some 
species which pass their 
earlier stages or entire lives in the water are preyed upon by 
aquatic birds." 1 

" Leading an active life as they do, birds require much 
food and are most ravenous enemies of insect pests. The 
various groups of birds differ so much in habits that they 




Courtesy of U. S. Bureau of Biological Survey 

Swallows 
Note position of toes of these birds when 
perching. Of what does the food of these 
birds consist? 



1 From Chapman's Bird Life. 
publishers. 



Used by permission of D. Appleton & Company, 



BIRDS AND HUMAN WELFARE 



419 



feed upon practically all groups of insects ; hardly an agri- 
cultural pest escapes their attacks. ... In feeding on 
insect pests not only do birds take a great variety, but they 
frequently destroy very large numbers. Often more than 
a hundred individuals are devoured at a meal and, in the 
case of small insects, 
sometimes several 
thousand. With 
such appetites it is 
not surprising that 
occasionally birds 
entirely destroy cer- 
tain insects locally. 
A number of cases 
are known in which 
trees, garden crops, 
and even farm fields 
have been entirely 
freed of insect pests 
by birds. On a 
200-acre farm in 
North Carolina it 
was found that birds 
were destroying a 
million green bugs 
or wheat aphids, 
daily." 1 

Usefulness of birds as destroyers of rats and mice. 
Hawks and owls with their hooked bills and claws are 
admirably fitted to clutch and tear living prey. It has been 
proved that the food of many of these birds consists almost 




Courtesy of Science Service 

Humming-bird feeding 

Ralph J. Ayer, farmer, Estonville, Colorado, and one 

of his tamed humming birds. 



1 From "Community Bird Refuges," Farmers' Bulletin No. 1239, United States 
Department of Agriculture. 



420 ANIMALS AND HUMAN WELFARE 



wholly of small gnawing mammals like field mice (111. p. 
394) and rats, which are exceedingly injurious to fields of 
grain. An examination of the stomachs of fifty short-eared 
owls showed that 90 per cent of them contained nothing but 
mice. Forty of the forty-nine stomachs of the rough-legged 

hawks (111. p. 422) that were 
examined were found to con- 
tain mice, while most of the 
rest contained injurious ani- 
mals. 

Usefulness of birds as 
destroyers of weed seeds. 
Another way in which birds 
are useful to man is in the 
destruction of weed seeds. 
Most perching birds that 
feed largely upon seeds {e.g. 
sparrows and finches) have 
strong conical bills, which 
are especially adapted for 
crushing seeds. Indeed all the sparrows, with the exception 
of the English sparrow, are useful in this way (111. p. 423). 
In one of the pamphlets of the United States Department 
of Agriculture, entitled " Some Common Birds and Their 
Relation to Agriculture," the writer estimated that in the 
state of Iowa during the six months of fall and winter tree 
sparrows devoured 875 tons of weed seed. An actual count 
of the stomach contents of a bobwhite showed the presence of 
400 pigweed seeds. In the stomach of another were 500 seeds 
of ragweed. It can thus be seen what enormous quantities 
of harmful plants are prevented from developing by birds. 

Some ways in which birds may be injurious to man. 
We have discussed briefly in the preceding sections some of 







SKf 






mi 

m 


mm 






i / . ' ™.^p 


>9W ' ™ 

} :' ' 


^^Wm^fy 



Hermit thrush 

What are two reasons why this bird is a 
desirable neighbor ? 



BIRDS AND HUMAN WELFARE 



421 



the ways in which birds are of incalculable value to man. 
It must be admitted, however, that some birds are of doubtful 
value while others are positively injurious. As an example 
of a bird, which, to say the least, is a nuisance, we may men- 
tion the common English sparrow (111. p. 424). This bird 
was first introduced from England into the United States at 
Brooklyn, New York, in 1851, 
because it was expected to at- 
tack some of our injurious in- 
sects. These sparrows have 
multiplied so rapidly that now 
they are found practically 
everywhere in the United States. 
As destroyers of harmful in- 
sects, these sparrows are prac- 
tically useless. Thus, for in- 
stance," the stomach of a single 
cuckoo (111. at right) was found 
to contain more injurious in- 
sects than did the stomachs of 
522 sparrows. 

But even more serious are 
the positive charges that have 
been proved against this bird. 
It pecks at and destroys the 
young buds of trees and later 

injures many fruits while they are ripening. It causes great 
losses in the grainfields from the time of planting to that 
of harvesting. Worst of all it molests and drives away our 
native song and insect-eating birds. 

Crows (111. p. 424), contrary to public opinion, are about 
as beneficial to the farmer as they are injurious : (1) They 
do much good by the destruction of injurious insects. 




Courtesy of U. S. Bureau of Biological Survey 

Yellow-billed cuckoo 

How is the bill adapted for catching 

insects ? 



422 



ANIMALS AND HUMAN WELFARE 



(2) They are beneficial by the destruction of mice and other 
rodents. (3) They are valuable occasionally as scavengers. 
On the other hand, (1) crows seriously damage the corn 
crop and injure other grain crops though usually to a less 
extent. (2) They are very destructive of the eggs and young 
of domesticated fowls and of wild birds. (3) They do harm 

by the distribution of seeds of 
poison ivy, poison sumach, and 
perhaps other harmful plants. 

While most of the hawks 
are undoubtedly beneficial, two 
species, namely, Cooper's hawk 
(111. p. 425) and the sharp- 
shinned hawk, must be kept 
down to limited numbers. Both 
of these are " chicken hawks, " 
and in addition they ruthlessly 
destroy great numbers of our 
most valuable wild birds. 

Some of the dangers that 
threaten bird life. Certainly 
enough has been said to show 
that, all things considered, birds 
are extremely useful to man. 
One would, therefore, expect that every possible means 
would be taken to protect all kinds of valuable birds. Yet 
what do we find? 

" Many valuable forms of wild life (especially of birds) have 
disappeared within recent years or are now being threatened 
with extinction. . . . Modern firearms, including repeating 
or automatic shotguns and rifles, give the hunter an immense 
advantage over the game. The automobile, better roads, ex- 
tension of rapid transit, and finally the airplane, enable the 



jS|% 






■>*v**!!$SK3| 












V »* ""' ' -"• -' 






Vv 






* "^^sSa 






rap v 






&m^ fir 2 * 






j0$wM!j*Ji^' 






4J|B^§t 






^^, t '. If 






%' vV 




\ 






\, •'■* 




"'; 


'" 









Courtesy of U.S. Bureau of Biological Survey 

Rough-legged hawk 
Why is this hawk useful ? 






BIRDS AND HUMAN WELFARE 



423 



hunter quickly to reach the most isolated places, and have 
greatly reduced the natural seclusion so essential to the wel- 
fare of many game animals. Furthermore, the game laws, in 
many states still de- 
fective, are the more 
easily evaded through 
the use of these means 
of conveyance. 

" Some conception 
of the extent to which 
shooting is carried on 
may be gathered 
from reports received 
through State Game 
Commissions, which 
indicate that the 
number of licensed 
hunters in the United 
States in 1929-30 
was more than 
6,900,000. To this 
number may be 
added at least 
1,500,000 represent- 
ing those who, hunt- 
ing on their own 
lands under the laws 
of certain states, 
require no license, and others who indulge in this sport 
illegally. This makes an impressive total of more than 
8,000,000 who go out with a gun every season." x 

1 From " Conserving Our Wild Animals and Birds" by Edward A. Goldman, of 
the United States Biological Survey, in Yearbook of the Department of Agriculture, 
1920. Statistics modified by Dr. W. H. Bell. 




Courtesy of U. S. Department of Agriculture 

Four common weed-seed eating birds 
i. Junco; 2. white-throated sparrow ; 3. fox spar- 
row; 4. tree sparrow. How are the bills of these 
sparrows adapted for crushing seeds ? 



424 



ANIMALS AND HUMAN WELFARE 




With such an army of hunters abroad in the land, it is 
easy to understand the dangers from this source that threaten 

bird life . In the early 
days of the white 
settlements in North 
America, game birds 
like the grouse and 
the duck were abun- 
dant and were of 
necessity killed, as 
were other wild ani- 
mals, for food. Later 
on began the killing 
of birds for sport. 
As the forests were 
cut down, the birds 
had less and less pro- 
tection ; and had not 
legislation inter- 
vened, the game birds would long since have been extermi- 
nated. 

Destruction of birds by 
cats. John Burroughs, the 
great naturalist and careful 
observer, declared that cats 
probably destroy more birds 
than all other animals com- 
bined. This statement is 
confirmed by the President 
of the National Audubon 
Societies, an organization 
that keeps careful census records of birds. Dr. Forbush, of 
the Massachusetts Board of Agriculture, stated that each 



Drawing by L. A. Fuerles 

The English sparrow 

Male above, female below. By what color markings 

could you distinguish the male from the female ? 




Courtesy of U. S. Bureau of Biological Survey 

The crow 






BIRDS AND HUMAN WELFARE 



425 



full-grown cat kills on the average at least 50 birds a year. 
He added the following : " Nearly a hundred correspondents, 
scattered through all the counties of the State (Massachu- 
setts), report the cat as one of the greatest enemies of the 
birds. The reports that have come in of the torturing and 
killing of birds by cats are absolutely sickening. The num- 
ber of birds killed by them in 
this State is appalling." x 

In order to check this de- 
struction of our useful birds 
it is necessary that the cat 
population should be con- 
trolled. All stray cats ought 
to be caught and painlessly 
killed. Since the value of cats 
as destroyers of rats and mice 
is more than doubtful, cats 
should not be kept in large 
numbers for any purpose. No 
cat should be allowed to roam 
at large during the nighttime 
when it is especially likely to 
steal upon its prey unawares. 

The effects of bird destruc- 
tion. While the esthetic loss 
to mankind resulting from the destruction of our wild birds 
cannot be computed, yet even in the cities this loss is realized 
as we see the song birds in the parks steadily diminishing in 
numbers. Every one, however, is affected by an increased 
cost of our food supply, and we have but to review the facts 
stated in the preceding sections to show that the destruc- 




Courtesy of U. S. Bureau of Biological Survey 

Cooper's hawk 

Has the upper bird caught a chicken or 

a wild bird ? 



1 From Useful Birds and Their Protection, by E. 
Department of Agriculture. Used by permission. 



H. Forbush, Massachusetts 



426 ANIMALS AND HUMAN WELFARE 



tion of our wild birds has a very important bearing on our 
everyday life. 

Every farmer knows that it is impossible to raise the 
crops of a single year without battling with insect pests. 
The time and expense involved in applying insect-destroying 

preparations would be 
difficult to compute, and 
even after the year's con- 
test the insects are often 
victorious. In ruthlessly 
destroying the wild birds, 
man interferes with the 
" balance of nature " and 
so helps the ravaging 
hordes of insects and 
gnawing animals and the 
weeds as well to multiply 
without adequate check. 
All this means that we, 
the consumers of the 
grains, the fruits, and 
the vegetables, must pay 
higher prices for the food 
we eat and for the clothes 
we wear. 

Protection afforded to 
birds by law. Fortu- 
nately the people of the United States have been awakened 
to the dangers that have threatened our bird life, and 
Congress and the state legislatures have enacted laws that 
have long been needed. This has been accomplished largely 
since 1913. In general it may be stated that with few ex- 
ceptions it is now against the law to kill at any time anywhere 




Courtesy of Science Service 

The passenger pigeon 

This bird has become extinct within the memory 

of men still living. 



BIRDS AND HUMAN WELFARE 427 

in the United States the insect-eating birds or to kill any of 
the game birds during the breeding season. 

In 1916 an important treaty was signed between the 
United States and England, the provisions of which protect 
537 kinds of migratory birds in our own country and Canada 
during their migrations north or south. " Under the migra- 
tory-bird treaty act, it is unlawful in the United States to 
hunt, capture, kill, possess, sell, purchase, ship, or transport 
at any time or by any means any migratory bird included 
in the terms of the treaty, except as permitted by regulations 
which the Secretary of Agriculture is authorized and directed 
to adopt, and which become effective when approved by the 
President. The act provides police and other powers neces- 
sary for its effective enforcement." x " The act of Congress 
approved February 18, 1929, makes provision to meet more 
effectively the obligations of the United States under the 
migratory-bird treaty with Great Britain, by lessening the 
dangers threatening migratory game birds from drainage and 
other causes, through the acquisition by purchase, gift, or 
lease of areas of land and of water to furnish in perpetuity 
reservations for the adequate protection of such birds." 2 

Scientific classification of birds. Modern scientific clas- 
sification divides the birds of North America into twenty 
groups or orders, all the birds of a given order resembling 
each other more or less in structure. The common names 
given to some of these orders are suggested by their habits. 
As examples, we may name diving birds (loon), long-winged 
swimmers (gulls and terns), scratching birds (hens, turkeys, 
and quails), birds of prey (eagles, hawks, and owls), and 
woodpeckers (downy woodpecker). The highest order, known 

1 Quoted from "Federal Protection of Migratory Birds" by George A. Lawyer, 
Bureau of Biological Survey, from Yearbook of the Department of Agriculture, 1918. 

2 United States Department of Agriculture, Biological Survey, August, 1931. 



428 ANIMALS AND HUMAN WELFARE 

as the perching birds, is divided into twenty-seven families, 
some of which are the crow family, the sparrow family, the 
warbler, and the thrush family. All these birds are specially 
adapted for holding to the limbs of trees, since the mech- 
anism of the leg is so arranged that the toes are automat- 
ically clutched to the support upon which the bird is 
sitting. 

QUESTIONS AND APPLICATIONS 

1. How do birds differ from other vertebrates? 

2. Name, locate, describe, and give the function of each of the kinds of 
organs found on the head of a bird. 

3. Discuss the value of birds as objects of beauty. 

4. How are the kinds and amounts of foods eaten by different kinds of 
birds determined? 

5. Give an account of each of the three ways in which wild birds are of 
most use to man, with examples and wherever possible with statistics. 

6. In what ways may some birds be injurious to man ? Give examples. 

7. State some of the dangers that threaten bird life. 

8. Discuss the slaughter of birds by cats ; by hunters in former years 
for millinery supplies. 

9. What should be done to check the destruction of birds by cats ? By 
hunters ? 

10. State some of the bad effects of bird destruction. How are all of 
us affected by this destruction of birds ? 

11. In what ways has protection by law been extended to birds? 

12. What have the United States and Great Britain together done to 
protect the migratory birds? 

13. In what ways can you help to protect birds and encourage them to 
breed ? 

14. Find out from the farmers in your locality which birds are com- 
monly regarded as beneficial and which injurious. Are any of their ideas 
incorrect from a scientific point of view? 

15. Secure the leg of a fowl; hold the tendon at the end and double 
the leg as the animal does when it is perching on a roost, and watch the 
effect on the toes. Why would this be of special advantage to a perching 
bird? See if you can determine how these movements are accomplished. 






REPTILES AND HUMAN WELFARE 



429 



16. Watch birds when they are building their nests. Do both male 
and female birds share in this work? What materials are used in nest 
building? 

17. How can you tell by looking at a bird whether its food largely con- 
sists of (a) seeds, (b) insects, (c) other birds, fish, or mammals ? 

18. Make a list of the birds in your vicinity that are (a) permanent 
residents, (b) summer residents, (c) winter residents. 

19. Which of the birds with which you are familiar have (a) the sweet- 
est songs, (b) the most brilliant plumage, (c) bird notes that are annoying? 

20. Find out why the number of birds in a given locality may 
be affected (a) by draining swamps to get rid of mosquitoes, (6) by cutting 
forest trees, (c) by removing from the roadside bushes that have berries 
which remain through the winter, (d) by fastening pieces of suet to trees, 
(e) by setting apart by law "bird sanctuaries." 

21. Name two birds introduced from Europe which have become a 
menace by their rapid breeding. Why was this not true of these birds in 
Europe ? 



PROBLEM 4. HOW ARE REPTILES AND AMPHIBIA 
RELATED TO HUMAN WELFARE? 

I Reptiles (Turtles, Snakes, and Their Relatives) 
The turtle. The body of a turtle may be divided into four 
regions ; namely, head, neck, trunk, and tail. The larger 
part of a turtle, the 
trunk, is covered by 
a shell, and to this 
shell the bony skele- 
ton is firmly united. 
The two pairs of legs, 
however, are freely 
movable, but can be 
drawn within the 

Shell for protection. Photographed at Zoological Park. 

_._- _ .. Courtesy of New York Zoological Society 

The toes of the feet A lizard 

are armed with Note scales and claws on toes. 




430 



ANIMALS AND HUMAN WELFARE 



sharp, curved nails, and the legs are covered with scales. 
The legs are used for walking (111. p. 210) and also for swim- 
ming. In some turtles the legs become broad and flat and 
are of but little use except for swimming. 

The head, neck, and tail can also be drawn into the shell. 
Scales cover the neck and part of the head. The jaws of 







" ''''** «-«SSflS 


^mJ- 


i£lr' ; 





Photographed at Zoological Park. Courtesy of New York Zoological Society 

Alligators 
In Reptile House, New York Zoological Park. 

the turtle, often called the beak, possess no teeth. The 
eyes, protected by the eyelids, the nostrils, and the ear 
openings, are readily seen. 

Turtles reproduce by means of eggs, which are compara- 
tively large. Turtle eggs are often used for food. These 
animals breathe throughout their entire life by means of 
lungs. 



1- 


> 


^ 


*&&0%&St5M^m^ 


^ 1 




• ^B 






f : ^WB^^ 



Photographed at Zo'ological Park. Courtesy of New York Zoological Society 

A snake with its eggs 




%; • V*^ 



r.^ - .**- 



Photographed at Zoological Pari,. Courtesy of New York Zoological Society 

A rattlesnake 

The young of this snake are born alive, while those of the snake in upper illustration are 
hatched from eggs that have been laid. 



432 



ANIMALS AND HUMAN WELFARE 



Relatives of the turtle. Animals related to the turtle are 
the lizards (111. p. 429), alligators (111. p. 430) and crocodiles, 
and snakes (111. p. 431), all of these animals being known 
as reptiles (rep'tilz). None of the reptiles, other than the 
turtles, possesses a shell, but all are covered with scales, and 
have toes armed with claws, except the snakes, which have 
no appendages. Unlike the turtles, other reptiles have jaws 
that contain sharp teeth, used in holding their prey, and 




Photographed at Zoological Part. Courtesy of New York Zoological Society 

Snake skulls 
At left note the large fangs of a rattlesnake. The poison is secreted in glands in the 
head and is ejected through a small opening near the tip of each fang. At right is the 
skull of a nonpoisonous snake. Note that all of the teeth point inward, thus preventing 
the escape of the prey. 

in the rattlesnake (111. p. 431), copperhead, water moccasin, 
and coral snakes, some of these teeth are provided with 
poison glands (111. above). The water moccasin and coral 
snakes are found only in the southern part of the United 
States and the copperhead in the northern part. The 
rattlesnakes are more widely distributed. None of the 
other reptiles in the United States is in any way dangerous 
to man. Indeed, many snakes destroy great numbers of 
rats and mice, while lizards catch large numbers of insects. 
The hide of the alligator is of considerable value for leather. 



AMPHIBIANS AND HUMAN WELFARE 433 



All reptiles breathe throughout their life by lungs, and most 
of them reproduce by eggs, which are hatched by the warmth 
of the sun (111. top, p. 431). 

Amphibians (Frogs and Their Relatives) 

Habits of frogs. There are many kinds of frogs, differing 
from one another considerably in size and color ; but all 
frogs live in places where 
water is more or less 
abundant. Frogs are 
often found either on 
the banks of ponds and 
streams or floating on 
the surface of the water 
with only the tip of the 
nose above water. In 
color they usually re- 
semble their surround- 
ings rather closely (111. 
at right) and so secure a 
certain degree of protec- 
tion from fishes, snakes, 
birds, and man, which are their more common enemies. 
When pursued, they quickly disappear beneath the water 
and often bury themselves in the mud at the bottom until 
the need of air compels them to return to the surface. 
Late in the autumn they burrow in the mud and remain 
there until the following spring. Because of their inactivity 
during this period little energy is required, hence frogs are 
able to secure whatever air they need through their slimy 
skin. The more or less pointed snout of the frog, its slippery 
skin, its long, muscular hind legs, with webbed feet all adapt 
the animal for rapid swimming through the water. 




Courtesy of American Museum of Natural History 

A frog 
Note that it resembles its surroundings. 



434 ANIMALS AND HUMAN WELFARE 

EXERCISE 64 

Structure and functions of a frog. Laboratory study. 

A. Regions and appendages. 

1. The frog's body consists of two principal parts, or regions; 
namely, the head and trunk. The line of union between the two regions 
is just in front of the anterior 1 appendages (arms 2 ). Which of these 
regions is the larger? 

2. Name and locate the organs that you find on the head, giving 
the number of each. 

3. Locate the appendages (arms and legs) attached to the trunk. 

B. Breathing organs. 

1. Describe the position of the nostrils on the head. 

2. Examine a preserved specimen in which a stiff bristle has been 
passed through one of the nostrils. 

a. Tell what was done. 

b. Into what cavity has the bristle emerged ? 

c. In what region (anterior or posterior) of the roof of the mouth 

cavity are the inner openings of the nostrils located ? 

3. (Demonstration by teacher using preserved specimen.) Just back 
of the tongue there is a narrow opening that leads into the windpipe 
(trachea) . This opening is called the glottis. 

a. Where is the glottis located ? 

b. Does the glottis extend lengthwise or crosswise of the mouth 

cavity? 

c. Into what does the glottis open? 

4. Examine a fresh frog dissected in such a way as to show the lungs. 

a. State the location of the lungs with reference to the head and the 

cavity of the trunk. 

b. Describe the color and appearance of the lungs. 

c. Insert the end of a glass tube, drawn out to a small diameter, into' 

the glottis opening and blow air into the lungs. Describe what 
you have done and state the result. 

5. Name in order the openings, the cavity, and the tube through 
which the air must pass in order to reach the lungs. 

1 The anterior part of an animal is the region at the head end ; the posterior at 
the hind end. 

2 The arms are sometimes called forelegs. 



AMPHIBIANS AND HUMAN WELFARE 435 

C. Breathing movements. 

1. Place a frog in a glass jar with an inch or two of water and watch 
the action of the floor of the mouth. This is one of the breathing 
movements. Describe this breathing movement of the frog. 

2. There are two breathing movements of the sides of the trunk : 
one a very active inward and outward movement and the other a 
very slight inward and outward movement. When you have seen 
these two kinds of movements of the sides, describe them and state 
which kind occurs the more frequently. 

D. How the frog exhales. 

1. What effect will the active inward movement of the sides have 
upon : 

a. The size of the body cavity? 

^b. The size of the lungs? 
c. The pressure of the air in the lungs? 
2. When the sides of the trunk move actively inward, will the air 
move into the lungs or out? Why? 

3. Through what passages will the air go from the lungs to the 
outside of the frog? 

E. How the frog inhales. 

1. When the floor of the mouth moves downward — 

a. Will the size of the mouth cavity be made larger or smaller? 

b. If the nostrils are now open, will the air move into the mouth 
cavity or out? Why? 

2. When the floor of the mouth is raised — 

a. Will the size of the mouth cavity be increased or decreased ? 

b. Will the pressure of the air in the mouth cavity be increased or 
decreased? 

c. If both the nostrils and the glottis are now open, in what direc- 
tions will air be forced ? 

d. What causes the slight outward movements of the sides of the 
trunk in the region of the lungs ? 

F. How the lungs are fitted for breathing organs. (Suggested as 
home work.) 

Note (to be studied). When the lungs are inflated (see B, 4), they 
look like bags (111. p. 441). The lungs are hollow, and their walls are 
composed of thin material. In these membranous walls are thin- 



436 ANIMALS AND HUMAN WELFARE 

walled blood vessels known as capillaries. The heart forces blood that 
has come from the body into these capillaries of the lungs and then 
back to the heart. 

1. Bearing in mind that respiration in all living things is essentially 
the same, state : 

a. What waste substance the blood brings to the lungs to be given 

off from the capillaries. 

b. What gas the blood in the capillaries takes up from the air in 

the lungs. 

c. How the walls of the lungs and of the capillaries of the lungs are 

fitted by structure to make this interchange of gases possible. 

G. Some adaptations for food getting. 

To the teacher. Select a number of preserved or freshly killed frogs of as large 
a size as you can get. Open the jaws as far as possible and keep them in this 
position by means of small pieces of wood. 

1. Seize the posterior or hind end of the tongue and pull it forward. 

a. Tell what you have done and state which end of the tongue is 

attached to the floor of the mouth. 

b. Describe the shape of the free end of the tongue. 

2. The living frog can extend its tongue much farther than you 
have been able to do in the case of the preserved frog, and in the living 
frog the tongue is covered with a very sticky substance. The tongue 
is used to catch insects at some distance from the animal (111. p. 440). 
Tell how you think the frog could use its tongue to catch insects and 
get them into its mouth. 1 

3. Look for teeth on the jaws of a skeleton of a frog ; or if you cannot 
obtain a skeleton, rub the finger over the jaws of a preserved specimen. 

a. Which of the jaws has teeth? 

b. Describe the location of the teeth on the jaw. 

c. State the shape and size of the jaw teeth. 

d. What is the probable use of the jaw teeth? 

4. Look on the roof of the mouth for two relatively large palate 
teeth. Rub the fingers over the surface of the palate teeth. 

a. Tell what you have done. 

b. What have you found out about the palate teeth? 

c. What is the probable use of the palate teeth ? 

1 If possible live frogs should be fed on meal worms, or other insects, and the 
feeding movements observed. 



AMPHIBIANS AND HUMAN WELFARE 437 

H. How a frog swallows. 

1. Gently touch the eyes of a living frog until it draws them into 
the head. Tell what you have done and observed. 

2. Look at the roof of the mouth of a preserved specimen while you 
push the eyes into the head. Tell what you have done and describe 
the effect produced in the roof of the mouth. 

3. How will the act of pulling the eyes into the mouth cavity be 
useful to a frog in swallowing? * 

/. Structure of arms and legs. Place a live frog in a glass jar at 
least half full of water to cause the animal to extend the hind legs, or 
make this study on a preserved frog. 

1. Make a sketch (natural size) of an arm to show the shape and 
size of its parts : upper arm, elbow, forearm, hand, number of fingers. 
Label each part. 

2. Draw one of the legs (natural size) to show the following parts : 
thigh (next the body), knee, shank, ankle (elongated region above foot), 
foot, toes, web between toes. Label each part. 

J. How a frog sivims. Place an active frog in a sink or other 
receptacle large enough to afford it room to swim. The water should 
be deep enough so that the frog will not strike the bottom with the 
legs. Get the frog to swim the full length of the receptacle as many 
times as may be necessary to answer the following : 

1. Tell what j^ou have done. 

2. Describe the movements of the hind legs in swimming. 

3. In which of these movements are the toes spread out? 

4. In which of these movements, therefore, can the frog get the 
best hold upon the water? 

5. In which direction must the frog push the harder in order to 
move in the direction that it does ? 

6. In what respects are the posterior appendages well fitted for 
swimming? 

7. In what respects are the anterior appendages not so well fitted as 
the legs for swimming ? 

K. How a frog jumps. Place a frog where there is plenty of room, 
and get it to jump as many times as necessary to answer the following : 
1. Tell what you have done. 

1 See footnote on the preceding page. 



438 ANIMALS AND HUMAN WELFARE 

2. Describe the position, of the parts of the legs just before the frog 
jumps. 

3. Describe the movements made by the parts of the leg in the act 
of jumping and in the act of landing. 

4. In which of these two movements must the frog use the greater 
force ? 

5. Which movement, therefore, throws the frog into the air? 

6. In what respects are the legs better adapted for jumping than 
the arms? 

L. Internal organs. 

To the teacher. Put into a covered jar enough frogs to supply each two students 
with a specimen. Put into the jar some ether, or, better, saturate a small sponge 
with the ether and place it in the jar. When the animals are dead, dissect them 
as follows : Lift up the skin of the ventral wall of the abdomen with the forceps ; 
carefully insert the point of the scissors near the posterior end of the trunk, and 
carefully cut forward along one side of the body as far as the tip of the head and 
back along the other side of the trunk, until the skin is completely removed from the 
ventral surface. In a similar manner remove the muscular wall that covers the 
trunk, being careful not to injure the internal organs. If time allows, remove 
also the skin from one leg ; call attention to the thinness of the skin and to the 
underlying blood vessels ; show the characteristics and action of the leg muscles. 
If the specimen is a female, remove nearly all the eggs and throw them away. 
Insert a blowpipe in the glottis and partly inflate the lungs. Wash the specimens 
thoroughly to remove all traces of blood and cover them with water in a dissecting 
pan. 

If the specimens are needed on successive days, they should be wrapped in a wet 
cloth immediately after the class work of each day and kept in a cold place. Use 
only specimens that are fresh. 

1. Make an outline drawing (natural size or twice natural size if the 
frogs are small) of the head and trunk regions of a dissected specimen, 
together with the base of each of the four appendages, and draw 
nothing else until directed to do so. 

2. The heart is a cone-shaped body midway between the arms. 
Draw the heart to show its position, shape, and relative size. 

3. On either side of the heart are the lungs. Stretch one of them a 
little by pulling on it ; then let it go. 

a. State whether or not the lungs are elastic. Are they hollow or 

solid? 

b. What is the color of the lungs ? State whether or not you find 

tiny blood vessels in the fresh lung. 

c. Draw the lungs so as to show their situation, size, and shape. 






AMPHIBIANS AND HUMAN WELFARE 439 

4. On the frog's right side and behind the heart and lungs is the 
reddish, several-lobed liver. Sketch in your drawing the liver to show 
it in position. 

5. On the frog's left side and under the liver in its natural position 
is a whitish, oblong body, which narrows at its posterior end. This 
body is the stomach. Push the handle of the dissecting needle down 
the gullet into the stomach. 

a. Tell what you have just done. 

b. What organ does the handle enter? 

c. Draw it in its natural position to show its shape and size. 

6. Extending from the stomach is a tubular structure of con- 
siderable length, the small intestine. At the lower end of the small 
intestine the tube becomes larger and then disappears between the 
two thighs. This last part of the tube is called the cloaca (klo-a'kd), 
or large intestine. Draw the small and large intestines as seen in 
position. 

7. Between the stomach and the first loop of the small intestine is 
a thin pink body, the pancreas, which is a very important digestive 
gland. Make a separate drawing of the stomach and the loop of the 
intestine to show the pancreas. 

8. Label : Heart, Lungs, Liver, Stomach, Small intestine, Large in- 
testine, Pancreas. 

9. Find two red bodies on either side of the spinal column. These 
bodies are the kidneys. The kidneys remove the nitrogenous waste 
(urea) from the blood. If the specimen is a male, note the orange- 
colored spermaries. If it is a female, note the position, appearance, 
and number of the eggs in the ovaries. Make a separate sketch of 
the kidneys and spermaries or ovaries twice the natural size and label 
each. 

10. Dissect out the whole alimentary canal, carefully cutting the 
membranes that hold together the coils of the intestine. Float the 
alimentary canal in a tray of water. Lay the liver over to one side and 
find between the lobes on the under side a thin-walled, green sac, the 
gall bladder or bile sac. Draw all of these parts and label the Gullet, 
Stomach, Small intestine, Large intestine, Lobes of the liver, Gall bladder, 
and Pancreas. 

Adaptations for food-getting and digestion. Frogs feed 
upon insects, fish, and other frogs, and even birds have been 



440 



ANIMALS AND HUMAN WELFARE 



found in their stomachs. Insects are caught by the aid of 
the slimy tongue, the tip of which can be thrust out of the 
mouth and then drawn back again with the insect adhering 
to it (111. below). This is accomplished so quickly that it is 
difficult to see the tongue movements. The tiny teeth 
that are found on the upper jaw and the two large teeth in 
the roof of the mouth are useful only in preventing the 
escape of the prey from the mouth. Hence the food is 
swallowed without being chewed, and after 
passing down the short gullet it enters the 
tubular stomach (111. p. 441), where it is 
partially digested by ferments secreted by 
certain cells found in the lining of this 
organ. 

When the food leaves the stomach, it 
enters the coiled small intestine where the 
process of digestion is continued by the 
bile secreted in the liver and the pancre- 
atic juice prepared in the pancreas. 1 As 
the digested food slowly moves along the 
small intestine, it is absorbed by the capil- 
laries (thin-walled blood tubes) in the 
mucous membrane of this tube and so 
may be carried by the blood to the various cells of which 
the body is composed. Digestion not only prepares the 
food for absorption but makes it ready to be used in the 
cells either for growth and repair or for the production of 
energy. 

Blood and circulation. The blood of the frog, when 
examined under the microscope, is seen to consist of two 
kinds of cells {red and white corpuscles) (111. p. 442), which 
are floating in a liquid known as plasma. The plasma con- 

1 Both of these digestive fluids are carried to the intestine by ducts. 




Frog catching an 
insect 



AMPHIBIANS AND HUMAN WELFARE 441 

sists largely of water and digested foods that have been 
absorbed from the alimentary canal. 

As in the human body, the circulatory system consists of 
the heart and three kinds of blood vessels ; namely, arteries, 
veins, and capilla- •->. 

fees. The heart F<m-<''j£ w(^\flk 

is located in the b ^ dn \ \jft #l\IAs, 
body cavity just brain "'^m M^^^^^ 
back of the head Hind--~W{ m^^^^^^^h^^ L ^ tliUl9 

two auricles and ^fM'^M^^^^^^^St\^' 

a ventricle (111. ^^\9^^^^^\^'' ston ^ fl 

p. 443). Asmight ^^^^^^^'f~~ Spermary 

U 9 pvnpptpf] this Large ^^^^^m^^~~ 

ue expeLieu, uiifc intestine i§^wl!H^sl Kidney 

makes necessary ^^^^m^^^M^K 

other differences /^^^^^^^^M 

i.i i j /^^^^^^^^ ' ■&£& Bladder 

in the circulatory /^^^^^^^^fe^V 

system of the VIST ^ usc ^ es °f 

frog. In the fish ^S^Slk thtgh UNR*" Openings of 

we shall find that Muscles °f^Sj^k I 4> 

OTffanS Of the Redrawn from a chart by R. Weber 

body Which the Organs of a frog 

blood has supplied with food and oxygen and from which 
the blood has received carbon dioxid. The right auricle re- 
ceives this blood brought from the body in three large veins. 



442 



ANIMALS AND HUMAN WELFARE 



Through two small veins the left auricle receives blood from 
the lungs, where the blood has given off the carbon dioxid 
and received a fresh supply of oxygen. 

The blood from both auricles now flows into the single 
ventricle, which then contracts and pumps the blood into a 
large artery. Certain branches carry the blood having the 

larger amounts of oxy- 
gen (i.e. the blood from 
the lungs) to the head, 
trunk, legs, and other 
organs of the body, while 
other branches carry the 
blood just received from 
the body, with its larger 
amount of carbon dioxid, 
to the lungs and the skin. 
In the thin-walled 
capillaries which connect 
the arteries and veins in 
every part of the body 
(111. p. 444) all the 
changes in the composi- 
tion of the blood take 
place. The capillaries just outside the mucous membrane of 
the stomach and the intestines absorb the digested food. The 
capillaries in the muscle tissues permit the escape from the 
blood of oxygen and food substances for use in the tissues and 
the absorption from the tissues of carbon dioxid and other 
wastes. 1 

1 The tail of a goldfish or tadpole is excellent for demonstrating the blood current. 
Wrap a goldfish or tadpole in wet cloth or cotton and support it so that the tail can be 
placed between two glass slides on the stage of the microscope. The space between the 
two slides should be kept filled with water. The movement of the corpuscles through 
the margin of the tail should be examined with the low power of the microscope. 




Blood corpuscles of a frog 
Magnified as seen through a microscope. How 
do these differ from human corpuscles ? (See 111. 
p. 114.) 



AMPHIBIANS AND HUMAN WELFARE 443 



Respiration and the liberation of energy. The walls of 
the frog's lungs contain a network of capillaries, and in these 
thin-walled tubes the red corpuscles absorb the oxygen that 
is forced into these sacs by the upward movement of the 
floor of the mouth. As we have seen, the blood with a 
fresh supply of oxygen flows from the capillaries of the lungs 
into the veins and so 
finally into the left 
auricle and thence into 
the ventricle. Here it 
tends to become some- 
what mixed with the 
blood (from the right 
auricle) which has just 
returned from the 
body. However, the 
structure of the heart 
and the arteries is such 
that the blood that 
has come from the 
lungs with a larger 
supply of oxygen is 
sent out by arteries to 
the head and all parts 
of the body. 

In the capillaries the oxygen is absorbed by the cells. 
Oxidation of the food and protoplasm takes place, and 
energy is thereby released, which enables the frog to ac- 
complish locomotion, secure its food, and perform all its 
destined tasks. The carbon dioxid and other wastes pro- 
duced by oxidation pass through the capillary walls into 
the blood and, as we have seen, are carried back to the 
right auricle of the heart and then to the lungs, where car- 



Arteries 
to head ' 

Right auricle v 

Artery to 
right lung ^ 
and skin 

Artery to y*j 
right foreleg 

Right lung y 

Arteries -*' 
to liver 
stomach 

and 
intestines 

Arteries ^^^y^" 
to hindlegs 




Artery to 
left lung 
and skin 

Artery to 
"'left foreleg 

"fC Left 

auricle 

"Left lung 
v Ventricle 

"Dorsal 
aorta 

Arteries 
to kidneys 

Kidneys 



A 

Arteries of a frog 

Compare this circulation with human circulation. 

(See 111. p. 128.) 



444 



ANIMALS AND HUMAN WELFARE 



w^^^^^^^^L bon dioxid is excreted - Other 
iJ^^^^^^^W™ wastes are excreted by the 
kidneys. 

The skin of the frog is like- 
wise permeated by a network 
of capillaries so that it acts as 
do the gills of fishes in absorb- 
ing oxygen from the water and 
in giving off carbon dioxid. 
While the frog is buried in the 
mud during the winter, it 
breathes entirely through the 
skin. So much does the frog 
depend on the skin as a breathing organ that, if the skin be- 
comes dry so that air cannot be absorbed, the frog dies. 




Pigment 
cells 

Red corpuscles 

Capillaries of a frog 
Note the countless corpuscles within 
each capillary and the irregular pig- 
ment cells which give the color to the 
skin. 




Eggs 



Egg 

containing 

young 

tadpole 



Tadpole with 

external 

gills 





Tadpole with 
internal gills 



dpole with 
hindlegs and 
forelegs 



Frog with tail 



Frog with forelegs 
and hindlegs 



Life history of a frog 
Which of the stages are lived wholly in the water ? 



AMPHIBIANS AND HUMAN WELFARE 445 



Reproduction and life history. In most of the animals 
studied thus far we have found special organs devoted to 
the process of reproduction ; namely, ovaries for egg pro- 
duction in the female and in the male spermaries that form 
the sperm cells. Before the egg cells can develop into 





Egg at 
two-cell stage 



Egg at 
four-cell stage 






Early blastula Section of blastula Late blastula 

(Many-celled stage) (Many-celled stage) (Many-celled stage) 

Cell division in the frog's egg 
How do the color and the size of the cells at the upper surface differ from those on 

the lower part ? 

embryos, each must be fertilized by a sperm cell. All the 
facts we have just stated apply equally well to the frog. 

Frogs' eggs are deposited in springtime in masses that 
float on the surface of the water. 1 Each fertilized egg is a 
small sphere, black on its upper surface and white beneath 
and inclosed in a gelatinous covering (111. p. 444). The 
warmth of the sun causes the one-celled egg to divide 
vertically in half to form the two-celled stage (111. above), 

1 If possible eggs in different stages of segmentation should be secured, preserved 
in 5 per cent formalin, and used for demonstration. 



446 



ANIMALS AND HUMAN WELFARE 



and the process of division continues until the egg consists 
of many cells (111. p. 445). Food for the development of 
the embryo is stored in the egg. 

The many cells of the egg gradually become different in 
character and so form the various organs of the embryo 
(111. p. 444). Soon after hatching, the young of the frog, 
known as tadpoles, secure their food by sucking in tiny water 

plants found on the sur- 
face of plants and stones 
(111. p. 182). Tadpoles 
resemble fishes in hav- 
ing gills for breathing, a 
heart with two chambers 
instead of three, and a 
tail for locomotion. At 
first the gills are on the 
outside of the body (111. 
p. 444), but later four 
pairs of internal gills are 
formed, and the external 
gills are absorbed. The 
animal increases in size, 
the hind legs appear (111. 
p. 444), and the forelegs are formed beneath the skin. 
Meanwhile the lungs are being developed, the heart becomes 
three chambered, the legs grow larger, arms appear, and 
finally the gills and the tail are completely absorbed. The 
tadpole now leaves the water, since it is an air-breathing 
animal. This succession of changes after hatching from the 
egg is known as a metamorphosis (met'd-mor'fo-sis). 

Relatives of the frog. Much like the frog in structure 
and life history is the common garden toad. Toads, how- 
ever, in their adult stage cover themselves more or less with 




Courtesy of American Museum of Natural History 

A toad 

In what ways does this resemble and differ 
from a frog ? (See 111. p. 433.) 



AMPHIBIANS AND HUMAN WELFARE 447 



dirt in the daytime and come out at night to feed upon 
insects, which constitute their sole food. Instead of having 
a smooth, slimy skin, as does the frog, a toad's skin (111. 
p. 446) is dry and covered with elevations commonly known 
as " warts." These elevations contain cells which secrete 
an irritating substance that protects the toad from animals 
that would prey upon it. There is no foundation, however, 




Photographed at Zoological Park. Courtesy of New York Zoological Society 

Salamanders (Newts) 
How do they differ from lizards in their structure and lif e habits ? 

for the popular notion that the warts of human beings are 
ever caused either by toads or frogs. 

In springtime toads seek the water in which to breed. 
The eggs, covered with a gelatinous substance, are laid in 
long strings instead of in masses, as is the case with frogs. 
The development and life history of the toad is much the 
same as that of the frog. As soon as metamorphosis is 
complete, the little toads leave the water and often are 
found considerable distances away from water. 



■ • 








lp ; ^ 






|; : illii:: 


li::: 


fefl% 




: : :v t 


wm % 




; 


H 




! 




■\ 


• 





Courtesy of American Museum of Natural History 

A spotted salamander 
How does this differ in structure from a lizard ? (See 111. p. 429.) 




Photographed at Zoological Park. Courtesy of New York Zoological Society 

A mud puppy (Necturus) 
Note the bunches of external gill filaments just behind the head. 



AMPHIBIANS AND HUMAN WELFARE 449 

Less like the frog, at least in the adult stage, are the sala- 
manders and newts (111. p. 447). These are found in damp 
places or in water and are often called " lizards" by those 
who do not know that a lizard has scales, claws on its feet, 
and breathes throughout its life by means of lungs. Some 
of the relatives of the frog, even after they have developed 
lungs, retain gills throughout their life (111. p. 448, below). 

Because of the ability of the animals described in this 
chapter to live both on the land and in the water, they are 
called Amphibia (from the Greek, meaning living a double 
life). 

Economic importance of the amphibians. None of the am- 
phibians, so far as is known, is harmful to man. On the 
contrary, all of them are more or less useful because of the 
insects they devour. This is especially true of the garden 
toad. It has been estimated by one author that a toad in a 
garden is worth nearly twenty dollars a year on account of 
the cutworms and other injurious insects that it destroys. 
In France the gardeners even buy toads to aid them in keep- 
ing obnoxious insects under control. Frogs, in addition to 
their value as insect destroyers, are of some value to man 
as food. 

A COMPLETION TEST 

The reptiles that are protected by a shell are the (1). All other rep- 
tiles are covered by (2) and have toes armed with (3) except the (4) which 
have no appendages. The jaws of all reptiles contain (5) except those 
of the (6). Many snakes are useful because they eat large numbers of 
(7) and (8) while lizards destroy many (9). The hide of the (10) is use- 
ful for leather. Four poisonous snakes are (11), (12), (13), (14). All 
reptiles breathe throughout their lives by (15), and most of them repro- 
duce by (16). Frogs belong to the class of vertebrates known as (17). 
Frogs and their near relatives are unlike reptiles because the skin has no 
(18) and the toes have no (19) and in the early stages of their development 
they all breathe by means of (20). A frog exhales by an inward movement 



450 ANIMALS AND HUMAN WELFARE 

of the (21) followed by the raising of the floor of the (22). A frog inhales 
by first lowering the (23) and then raising it. The glottis is an opening 
into the (24). The lungs of a frog are adapted for interchange of gases 
because the walls are (25) and they contain (26). The frog can catch 
insects by extending its (27) which is quite (28) so that the insect is caught 
and carried into the (29) . A frog can swim rapidly by means of the (30) 
which are long and have powerful (31) . The toes are also (32) . Two rela- 
tives of frogs are (33) and (34) that look somewhat like lizards but they 
have no (35). All Amphibia are useful because they devour (36). The 
amphibian that is most useful in this way is the (37). 

PROBLEM 5. HOW ARE FISHES RELATED TO HUMAN 

WELFARE ? 

Characteristics of Fishes 

What a fish is. In the minds of many people fishes 
include a number of animals which even a superficial study 
shows cannot be at all related to one another. Thus, for 
instance, animals as diverse as the jellyfish (111. p. 384), 
starfish (111. p. 451), shellfish (oysters and clams, 111. p. 535), 
and crayfish (111. p. 526) have nothing in common with real 
fishes except that they live in the water. Even whales (111. 
p. 14), seals, and porpoises are regarded by those who are 
ignorant of natural history as belonging to the fish class, 
because these animals spend their lives in the water and 
in some cases resemble fishes in shape. The question now 
arises — What are the characteristics of a true fish ? To 
answer this question we shall quote from one of the greatest 
authorities on fishes, Dr. David Starr Jordan. 

" A fish is a backboned animal which lives in (that is, 
under) the water, and cannot ever live very long anywhere 
else. Its ancestors have always dwelt in water, and likely 
its descendants will forever follow their example. So, as 
the water is a region very different from the fields or the 
woods, a fish in form and structure must be quite unlike 



FISHES AND HUMAN WELFARE 



451 



all the beasts and birds that walk or creep or fly above 
ground, breathing air, and being fitted to live in it. There 
are a great many kinds of animals called fishes, but in this 
all of them agree : All have some kind of backbone, all of 
them breathe their life long by means of gills, and none 
of them have fingers 
or toes with which 
to creep about on 
land." l 

When we apply 
these tests to each of 
the animals named in 
the first paragraph, 
we find every one 
lacks one or more of 
the characteristics we 
have enumerated. 
Thus, for instance, 
no jellyfish, starfish, 
shellfish, or crayfish 
has a backbone, even 
though all of them 
breathe by gill-like 
structures. Whales, 
seals, and porpoises, 
while they have back- 
bones, never breathe by gills ; instead, they must come to 
the surface to breathe air by means of lungs. 

Regions and appendages of the yellow perch. One of the 
commonest fishes found in fresh water over a large section of 
the United States is the yellow perch. A study of the yellow 




The under side of a starfish 

The animal's mouth is in the center of the star ; a 
single eye spot is at the tip of each of the five rays ; 
the projections on the ray at the right are the elon- 
gated sucking tube feet with which it carries on loco- 
motion. The other tube feet are seen retracted 
within the hard skeleton. 



1 From Jordan's Guide to the Study of Fishes, IX, 3. 
Appleton & Company, publishers. 



Used by permission of D. 



452 



ANIMALS AND HUMAN WELFARE 



perch (111. below) shows that the body is divided into three 
regions ; namely, head, trunk, and tail. Unlike the body of 
many animals, it has no neck, and the head, therefore, 
is joined directly to the trunk. The line of union is the hind 
margin of movable flaps, called gill covers, on the sides of the 
head. Just behind the gill cover on each side of the trunk 
is a paddlelike organ called the pectoral fin. On the under, 



Anterior dorsal fin - 
Pectoral fin N 



Left 
nostrils 



Posterior dorsal fin 
Tail fin 




Gill cover 




^m—Pelvicfin 



— Trunk 



Tail 



11 J 



Regions and appendages of a yellow perch 

or ventral, surface, below the pectoral fins, is a second pair 
which are known as pelvic fins. The pectoral and pelvic 
fins are known as the paired fins. Besides these there are 
several unpaired fins. On the top, or dorsal, surface are 
two dorsal fins, one behind the other, which project upward. 
Below the hind dorsal fin, on the ventral surface, is another 
single fin, called the anal fin. The tail region is considered 
to begin just in front of the anal fin, since in the fish the 
body cavity that contains the important organs of diges- 
tion, circulation, excretion, and reproduction ends at this 
point (111. p. 454). The anal fin, therefore, and also most 






FISHES AND HUMAN WELFARE 453 

of the posterior dorsal fin are attached to the tail region. 
At the posterior end of this third or tail region is the broad, 
forked tail {caudal) fin. 

EXERCISE 65 
Study of the external structure of a goldfish. Laboratory study. 

Materials: A living goldfish in a battery jar or small aquarium, if 
possible one for each student. Goldfish may be kept indefinitely in a 
glass jar with green water plants. The latter supply the fish with both 
food and oxygen. 

1. Compare the living goldfish with the yellow perch (111. p. 452). 
What differences do you notice in the position, number, and arrange- 
ments of the fins, and also in the number of nostrils ? 

2. Make an outline drawing (about five inches long) with sharp 
lines of the side view of the goldfish to show the shape and relative 
size of the three regions, and the position and shape of the organs of 
the head, and the various kinds of fins, in a manner similar to the illus- 
tration on page 452. Label each of the three regions of the body, the 
various organs found on the head, and the paired and the unpaired 
fins found on the body and on the tail. 

Locomotion of fishes. Many fishes, like the goldfish and 
the perch, are able to maintain a given position while they 
are at rest. This is made possible by means of an internal 
organ known as the air bladder (111. p. 454). The air bladder 
may be compressed and thus decreased in size, permitting 
the fish to sink, or it may be expanded, causing the animal to 
rise. Since, therefore, the fish is poised in a liquid medium, 
it is only necessary to overcome the resistance of the water 
about it in order to move in any direction. This resistance 
is more easily overcome, first, because the head is somewhat 
pointed like the prow of a boat ; second, because the over- 
lapping scales point backward ; and, third, because the 
whole body is covered with a slimy mucus, which makes it 
easy for the animal to slip through the water. 



454 



ANIMALS AND HUMAN WELFARE 



One who is at all familiar with a canoe knows that it would 
be very difficult to propel it by the use of a slender rod. One 
must have a paddle with the lower end broad and flat so 
that sufficient force can be expended against the water to 
cause the canoe to move. This is likewise true of the fish 
In swimming the fins of the fish act more or less like paddles. 
The broad, flat surfaces of these fins press against such an 



Stomachs 



/Air b /adder 
t Reproductive organs 



^H< 



^ 



Giii rakers' i / 
4 67//S* 

Heart', 
Liver' 


V \ ; / 
Intestines' 






M 




Internal 


organs 


of 


a fish 



amount of water that the animal is enabled to exert force 
enough to push its body in any desired direction. 

If one watches a goldfish 1 swimming slowly about in an 
aquarium, one would think that the paired fins, especially 
the pectoral fins, were the important swimming organs. 
But careful experiments have shown that this is not the 
case. When the goldfish has occasion to move more rapidly, 
the paired fins are not used at all but are pressed close to the 
sides of the body. In rapid locomotion the fish is driven by 

1 While studying this section, the pupils should watch the live goldfish when it 
is swimming both slowly and rapidly. Notice that each fin is composed of stiff 
fin rays and thin connecting membranes, and can be spread out or closed up somewhat 
like a fan. 



FISHES AND HUMAN WELFARE 455 

the movements of the tail and of the tail fin. The paired 
fins and the dorsal and anal fins seem to be used principally 
in steering the animal. The energy necessary for swimming 
is developed in the powerful muscles of the tail and trunk. 

EXERCISE 66 

How are the teeth of a fish adapted for food getting? Laboratory 
study. 

Open the jaws of a fresh or of a preserved fish. (Fish of large size, 
e.g. bass or cod, should be used if possible, the jaws being held wide 
open with pieces of wood.) Look for teeth on the jaws and on the 
roof of the mouth. 

1. State the location of the teeth and give some idea of their 
number. 

2. Rub the fingers gently back and forth over the teeth. Do they 
point backward or forward ? How do you know ? Describe any other 
characteristics of the teeth. 

3. Of what use would the teeth be in catching and holding other 
fish for food? 

Adaptations of fish for food getting. Unlike plants, 
fishes cannot make their food from materials found in the 
water, soil, and air, but must secure it ready-made in the 
form of plants and animals. The goldfish, for example, 
depends largely on vegetable food, while the cod 1 and the 
perch for the most part feed upon other animals smaller 
than themselves. Since these fishes must catch and hold 
their prey, their jaws are provided with many sharp teeth 

1 "The cod is omnivorous, and feeds upon various kinds of animals, including 
crustaceans, molluscs, and small fishes, and even browses upon Irish moss and other 
aquatic vegetation. All sorts of things have been found in cods' stomachs, such 
as scissors, oil cans, finger rings, rocks, potato parings, corncobs, rubber dolls, 
pieces of clothing, the heel of a boot, as well as other new and rare specimens of 
molluscs and Crustacea." — From American Food and Game Fishes, by David 
Starr Jordan and Barton Warren Everman, copyright 1902, and reprinted by 
permission from Doubleday, Doran and Company, Inc., publishers. 



456 ANIMALS AND HUMAN WELFARE 

that point backward and so prevent the escape of any active 
animal which may have been caught. The cod has teeth in 
the roof of the mouth and in the throat in addition to those 
found on the jaws, thus making more secure its hold upon 
its prey. 

Certain fishes subsist on small plants and animals, and 
therefore some means is needed by which the water taken 
in with the food may be rejected, while at the same time 




Courtesy of U. S. Bureau of Fisheries 

Goosefish or angler 
Observe the lure bait projecting from the top of the head. 

the food is retained. Hence, fishes are provided with a 
straining apparatus on the floor and the sides of the mouth 
cavity, which permits the water to escape when the mouth 
is closed. When the mouth is closed, the water is forced 
out and the small forms of life that the fish has secured are 
retained. Of this adaptation for food getting, we shall learn 
more in our study of the breathing organs (gills). 

Most of the fishes that prey on other animals secure their 
victims by dint of their speed. Some of them, however, 
are provided with lures (111. above) that may be luminous 
organs or tufts of filaments. Some fish have a color or 



FISHES AND HUMAN WELFARE 457 

pattern of coloration that serves to conceal them and per- 
mits their prey to approach without fear. Still others have 
means of wounding or disabling their prey before taking it 
into their mouths. But whatever a fish feeds upon and 
however it secures its food, plants and other animals must 
furnish the food substances required to make living matter 
and to furnish the fuel needed to develop the energy for 
the various activities of the fish. 

Adaptations of fish for digesting its food. In fishes, as 
in man, a portion of the body known as the digestive system 
is devoted to preparing the food for absorption and use. 
This digestive system consists of a food tube called the ali- 
mentary canal and certain groups of cells that form the diges- 
tive glands. When the fish swallows food, this passes from 
the mouth cavity into a short tube called the gullet and thence 
into a comparatively long and wide stomachy which in the 
perch extends half the length of the body cavity (111. p. 454). 
From the stomach extends the small intestine, which turns 
upon itself several times, forming a coil, at the hind end of 
which is an opening to the exterior just in front of the anal fin. 

In the inner lining of the stomach and intestine are di- 
gestive glands that have the power to manufacture digestive 
ferments and juices, which are poured out into the alimentary 
canal when food is present. These ferments make the foods 
soluble and ready for use in the body. In addition to the 
digestive glands in the lining of the alimentary canal, there 
is a large and very important gland that is situated outside 
the digestive tube. This gland is the liver, which secretes 
the bile. This is carried to the intestine by a tube called the 
bile duct. When the food has been digested, it is absorbed 
by thin-walled blood vessels (capillaries) found in the lining 
of the alimentary canal ; and so the food passes into the blood 
to be distributed to the various parts of the body. 



458 



ANIMALS AND HUMAN WELFARE 



Blood and circulation of blood in the fish. In the fish, as 
in man, there are blood vessels to distribute food and oxygen to 
the working organs (111. below) . A muscular heart, which aids 
in keeping the blood in constant motion through the blood 
vessels, is also present. The blood vessels are of three kinds ; 
namely, arteries, capillaries, and veins. The arteries have 
elastic walls which contract and so aid the heart in forcing 
the blood along its course. The arteries, as in man, always 




Circulation of blood in a fish 
Arrows indicate direction of flow. Beginning at the heart, trace course of blood 
to head, digestive organs, and muscles, and back to the heart. Through what organs 
does all this blood pass ? 

carry the blood away from the heart, and they subdivide 
into smaller and smaller tubes. At the ends of the smallest 
arteries are tiny, short, thin-walled blood vessels, the capil- 
laries. These permit the digested food to diffuse through 
their walls into the adjacent cells and absorb waste matter 
from the cells into the blood (111. above). Capillaries in the 
gills as in the lungs of man permit the excretion of carbon 
dioxid from these organs. 

The blood passes from the capillaries into the veins, which 
are thinner-walled than the arteries. The veins carry the 
blood back to the heart. The heart (111. p. 462), unlike that 
of man, consists of only two principal parts : a thin-walled 
receiving chamber, the auricle, which takes in the blood 



FISHES AND HUMAN WELFARE 459 

brought by the veins, and a thick-walled, muscular portion, 
called the ventricle, which forces the blood out into the 
arteries. 

EXERCISE 67 

How are fishes adapted for breathing? Laboratory study. 

1. Raise the gill covers of a fresh or preserved fish and find the 
gills, the breathing organs. Carefully separate the gills, either with 
forceps or a thin strip of wood, and count them. 

a. Tell what you have done. 

b. State the situation of the gills with reference to the gill covers. 

c. How many gills are found on each side of the fish? 

2. The passages between the gills are the gill clefts. Gently push 
a thin strip of wood or the forceps through one of the gill cLefts, and 
then open wide the jaws of the fish and look into its mouth. 

a. State what you have just done. 

b. In what cavity does the strip of wood or the forceps appear? 

c. What is the position of the gills with reference to the mouth 
cavity ? 

d. What are the gill clefts? 

3. Place a gill that has been removed from a perch or other good- 
sized fish in a small glass dish and cover it with water. Find the 
following parts of a gill: (1) a single firm curved portion known as 
the gill arch; (2) numerous closely packed divisions extending from 
the convex edge of the gill arch, called gill filaments ; and (3) projec- 
tions from the concave side or from the flat side of the gill arch, either 
in the form of ridges or somewhat long, slender teeth — the gill rakers 
or gill teeth. 

a. Tell what you have done. 

b. Name the three parts of the gill of a fish. 

► c. Separate the gill filaments with forceps or your fingers and ex- 
amine the inner surfaces. Describe the shape of one filament to 
show that it is not at all like a thread, as the name " filament " 
implies. 
d. Are the gill rakers in the specimen you are studying shaped like 
ridges, or like teeth, or are both kinds present? 

e. Which is composed of firmer material, the gill arch or the gill 

filaments? 



460 ANIMALS AND HUMAN WELFARE 

/. Which of the three parts of a gill is best fitted to act as a support 
for the other two ? Which part would expose to the water the 
most surface for the absorption of oxygen and the giving off 
of carbon dioxid ? Which might act as a strainer to hold food 
in the mouth while allowing water to pass through the gill 
clefts? 

g. Make a sketch (natural size) of the gill you are studying, 
labeling each part and the drawing as a whole. 

4. Suppose the same water remained on the gill filaments of a live 
fish for a minute — 

a. What gas will be absorbed by the gill filaments ? 

b. What change in the amount of oxygen dissolved in the water 

would therefore occur? 

c. What gas will be given off to the water from the gill fila- 

ments ? 

d. What change in the amount of carbon dioxid in the water will 

occur? 

e. State two positive reasons why it is necessary that currents of 

water should at intervals pass over the gill filaments. 

5. Describe the regular movements of the jaws and gill covers of 
a live goldfish. These are the breathing movements. In what life 
process will these breathing movements be useful to the animal? 

6. When the goldfish opens its mouth — 

a. Will the size of the mouth cavity be greater or smaller than 

when it is closed ? 

b. Why will the water enter the mouth when it is opened? 

c. What gas needed in respiration will the current of water bring 

into the mouth cavity? 

7. When the goldfish closes its mouth — 

a. Will the size of the mouth cavity be greater or less than when 

open? 

b. What will become of most of the water in the mouth? Give the 

reason for your answer. 

c. What gas needed in respiration will this current of water bring 

to the gill filaments ? What gas will the same current of water 
carry away from the gill filaments through the gill clefts ? 

How breathing and the release of energy are accomplished 
by fishes. Many other kinds of animals besides fishes have 



FISHES AND HUMAN WELFARE 461 

gills. Some of the other animals that breathe by gills are 
clams, oysters, crabs, lobsters, marine worms, and starfishes. 
Now you should know that all these animals, as well as fishes, 
live under water and cannot live out of water very long at a 
time, because they would be unable to breathe. Gills are 
breathing organs that are specially adapted for securing 
oxygen from the water, since they must be kept moist in 
order to permit the osmosis of oxygen and carbon dioxid. 

The parts of the gills in fishes that are well adapted for 
absorbing oxygen from the water and giving off carbon dioxid 
are the gill filaments. As you have already discovered, the 
gill filaments are very numerous, which is, of course, a great 
help in securing sufficient oxygen. But there are other 
peculiar features that are just as important. One of these 
is their shape. You doubtless thought at first sight that 
each filament was shaped like a thread, which is what the 
word " filament " literally means. But as you found out on 
more complete examination, each filament is a rather broad 
structure, somewhat like a triangular leaf, and very thin, 
thus affording more surface for the absorption of oxygen. 
But that is not all. Inside of the thin-walled filaments there 
are thin-walled blood vessels, capillaries, which are absolutely 
essential for the interchange of the gases oxygen and carbon 
dioxid. Let us now see how oxygen is brought to the gill 
filaments and how carbon dioxid is taken away from them. 

When a goldfish, or any other fish, opens its jaws, the 
mouth cavity will be practically empty for the moment. 
Consequently the water which surrounds the fish will force 
its way in and fill the mouth cavity. As the fish closes its 
mouth, the walls of the mouth cavity will exert a pressure 
on the water in the mouth sufficiently great to force the 
water through the gill clefts out beneath the gill cover into 
the surrounding water. The fact that every time the gold- 






462 



ANIMALS AND HUMAN WELFARE 



f \ Artery to rf{,/ m JUaments Veins 



fish closes its mouth the gill covers open is proof that water 
is being forced against the gill covers, thus opening them. 
As the water from the mouth cavity passes over the gills, 
the blood in the capillaries of the gill filaments absorbs 
oxygen from the water, and gives out carbon dioxid, and 
the stream of water carries the carbon dioxid to the outside. 

Now what becomes 
of the oxygen ab- 
sorbed by the blood 
in the filaments ? 
(111. at left.) 

As we have said 
before, the blood in 
the capillaries of the 
filaments is forced 
by the heart into 
arteries which ex- 
tend to all parts of 
the body. From the 
smallest arteries the 
blood with its cargo 
of oxygen enters the capillaries of the body, and here the 
blood gives up its supply of oxygen to the cells. In the 
cells the digested foods that contain carbon are oxidized and 
thus energy is released, and carbon dioxid is produced. The 
carbon dioxid is absorbed by the blood in the capillaries, 
and flows with the blood into the veins back to the heart and 
thence by arteries to the capillaries of the gill filaments. It 
then passes out through the thin walls of the capillaries and 
the thin walls of the filaments into the surrounding water, and 
is carried away by the current of water passing over the gills. 
Thus we see how a fish takes oxygen into its body and how 
it gives off carbon dioxid, which processes together consti- 




Artery to gills ^~" Valves 

Circulation of blood in a gill 

What kind of blood vessels are found in gill filaments ? 

Why is this an advantage in the breathing process ? 



FISHES AND HUMAN WELFARE 



463 



tute breathing. We also see that this process would not be 
of any use to the animal unless the foods were oxidized and 
energy thereby released to enable the fish to carry on its 
varied activities. All these processes, as in other animals, 
make up the whole process of respiration. Do not forget, 
however, that the release of energy from foods is the 




Courtesy of U. S. Bureau of Fisheries 

Salmon jumping falls 
What organs in the fish enable it to make these leaps ? 

most important part of respiration. Without that all the 
rest would be useless to a fish, or to any other living 
thing. 

Reproduction and life history of the salmon. 1 The Pa- 
cific salmon (111. p. 468) are caught in the rivers that flow into 
the Pacific Ocean, such as the Columbia, Sacramento, and 
the Yukon. The salmon reach their maturity in the ocean. 

1 For a general account of reproduction in fishes see pages 212-217. 



464 ANIMALS AND HUMAN WELFARE 

When, however, the spawning time approaches, the salmon 
make their way in great numbers to the mouths of the rivers. 
They then proceed up the streams, leaping seemingly im- 
passable waterfalls to reach the headwaters (111. p. 463). 
Here on sand or gravel the female salmon deposits her eggs, 
and the male covers them with the fertilizing sperm cells. 
The fertilized eggs are then covered with sand or gravel and 
thereafter receive no attention from their parents. Indeed, 




* :it *^zm^?r^^ 



, Courtesy of U. S. Bureau of Fisheries 

An eel 
What fins can you find ? 

the parent fishes soon die, none of them ever reaching the 
ocean again. After the eggs hatch, the young develop 
slowly and finally go down the stream to the ocean to repeat 
the life of their parents. 

Reproduction and life history of the common eel. Until 
recent years nothing was known concerning the marvelous 
life history of the eel (111. above). Even now there are gaps 
in our knowledge regarding the breeding habits of this fish, 
in spite of the fact that young and mature forms have been 
known from ancient times. Upon reaching maturity the 
eels leave the fresh-water streams and seek the ocean to 



FISHES AND HUMAN WELFARE 465 

spawn. Hence their course to their spawning grounds is 
directly opposite to that of the salmon. 

Concerning their egg-laying habits, however, we as yet 
know nothing beyond the fact that the eels of Europe and 
America swim far out to the mid-Atlantic to deposit their 
eggs. We know this because the youngest eels are never 
found near land or anywhere near the mouths of rivers which 
they finally enter to complete their development. Young 
and larval eels have been collected by means of fine-meshed 
towing nets from regions all the way across the North Atlantic 
from the latitude of Florida to Maine. The youngest speci- 
mens, however, are found only in mid-ocean, especially 
between the Azores and Bermuda. From here they some- 
how make their way for a thousand miles or more, till finally 
they reach the mouths of rivers of Europe and America. 
This long journey requires several years. Yet during a 
portion of this period at least the young eels take no food 
whatever. Indeed, after attaining a certain size, they 
actually become smaller ! 

The Relation of Fishes to Human Welfare 

Fishes in relation to human welfare. From very ancient 
times fishes have formed a considerable part of the food of 
peoples that lived near bodies of water. The importance 
to man of fishes as a source of food can hardly be over- 
estimated. Unlike domestic animals, fish grow to maturity 
without any care on the part of man. The fisherman has 
only to provide the means for gathering his harvest, while 
the herdsman must care for his flocks and herds the year 
round. Thus we see why it is that fish should be a cheaper 
form of food than the flesh of domesticated animals. Nearly 
all parts of fish are used as food. Not only is the flesh eaten, 
but also the eggs (roe) (111. p. 217). These animals furnish 



466 



ANIMALS AND HUMAN WELFARE 




food either in a fresh condition or when prepared in various 
ways. Among these methods of preservation are drying, 
smoking, pickling, and canning. 

While fish are important to man as a source of food, they 
have still other uses. Thus, for instance, menhaden are 
caught scarcely at all for food but for the large quantities 
of oil extracted from them. The remainder of their bodies 
is used as fertilizer, or after being dried and ground it is fed 

directly to cattle and to 
other domestic animals. 
More than 3,000,000 
gallons of oil and about 
50,000 tons of fish meal 
and scrap, with a total 
value of $3,000,000, are 
obtained annually by 
American fishermen 
from this kind of fish. 
The oil extracted from 
the livers of cod is a 
good source of vitamins A and D for use in nutrition. In- 
cidentally, other fish oils, such as salmon, sardine (California 
pilchard), burbot liver, menhaden, tuna, and herring are 
especially good or better sources of one or both of these 
vitamins for use in nutrition. The air bladders of many 
fishes (e.g. sturgeon and cod), when dried, yield a high grade 
of gelatin. 

Importance to man of salmon and codfish. Salmon (111. 
p. 468) and herring are the most valuable food fishes of the 
world. The Pacific salmon, of which there are five species, 
is our most important fish. The Atlantic salmon, though 
once abundant, has disappeared from all the Eastern coast, 
save in the Penobscot River. Most of the catch of salmon 



A flounder 
Note that both eyes are on one side of the fish. 
In its early life it swims through the water and 
the left eye is on the left side. When it comes to 
lie on the bottom this eye moves through the skull 
to the position shown in the picture. 






FISHES AND HUMAN WELFARE 467 

is canned, although large quantities are mild-cured, smoked r 
and frozen, and much is marketed fresh. The catch of the 
Pacific salmon in 1930 was valued at $16,022,000, and the 
value of the salmon after it was canned was nearly $40,000,000. 
Of considerable importance, at least in the United States, 
is the cod (111. below), for which the fishermen receive annu- 
ally about $3,700,000. Other countries engaged in the cod 




_ ._ , Courtesy of U. S. Bureau of Fisheries 

Codfish 

How many pairs of fins and how many unpaired can you see? The white line is 
formed by the lateral line sense organs. 

fishery are Newfoundland, Canada, Norway, Sweden, Great 
Britain, France, and Japan. Codfish are found in the north- 
ern part of both the Atlantic and the Pacific oceans and are 
usually caught at a depth of 150 to 500 feet. " From the 
earliest settlement of America, the cod has been the most 
valuable of our Atlantic coast fishes. Indeed the codfish 
of the Banks of Newfoundland was one of the principal 
inducements which led England to establish colonies in 
America, and in the records of early voyages are many refer- 
ences to the abundance of codfish along our shores. . . . 



468 



ANIMALS AND HUMAN WELFARE 



So important was the cod in the early history of this country 
that it was placed on the colonial seal of Massachusetts, and 
it was also placed upon a Nova Scotian bank note, with the 

legend 'Success to 
the Fisheries.' v l 

The average 
weight of large cod 
is from twenty to 
thirty-five pounds. 
The average weight 
of small cod is twelve 
pounds. While cod 
weighing 75 pounds 
are not common, one 
was caught off the 
New England coast 
many years ago that 
weighed 21 Impounds. 
Cod is marketed 
fresh, frozen, pickled, 
salted, canned, and 
dried. Oil and isin- 
glass are also ob- 
tained from the cod. 
Reckless destruc- 
tion of our supply 
of food fishes. The 
American people 
have been exceedingly reckless in the destruction not only 
of our forests (p. 311), but also of our resources of wild life 




Courtesy of U. S. Bureau of Fisheries 

Removing salmon from floating trap in Alaska 



1 From American Food and Game Fishes, by David Starr Jordan and Barton 
Warren Everman, copyright 1902, and reprinted by permission from Doubleday, 
Doran and Company, Inc., publishers. 



FISHES AND HUMAN WELFARE 469 

on land and in the water. We have cited the way in which 
the Atlantic salmon has been nearly exterminated. More 
than a hundred years ago this fish was so abundant and so 
commonly used that young men in agreeing to work for an 
employer insisted that they be given salmon to eat no oftener 
than twice a week ! 

Soon after the Revolutionary War the number of these 
fishes began to diminish rapidly, and in 1819 one writer 
states that the salmon had scarcely been seen in the Con- 
necticut River for fifteen or twenty years. The principal 
reason for this was that high dams were built across the 
rivers, which prevented the fish from swimming up streams 
to their fresh-water spawning places. The Pacific salmon 
(111. p. 468) are decreasing in some localities, but in other 
places, particularly in Alaska, they are more than holding 
their own, due to conservation measures. 

How our supply of fishes can be conserved. Nearly all of 
the states have passed laws for the protection and conserva- 
tion of game fishes, such as trout and bass ; the sportsmen 
have seen to this. While it is desirable that these forms of 
wild life, which are also a source of food supply, should be 
preserved and their number increased, it is of much greater 
importance that the fishes which supply food for millions 
should not be left without adequate protection. 

The number of all fishes desirable for food should be 
increased by artificial propagation (111. p. 214), and wise 
laws governing the catching of fish should be passed and 
rigidly enforced. The United States Government and vari- 
ous states have been doing splendid work in the artificial 
propagation and distribution of fishes through the agency 
of the fish-hatching stations of the Bureau of Fisheries and 
of the states. In 1930 the United States Bureau of Fisher- 
ies distributed a total of over seven billion eggs, fry, and 



470 ANIMALS AND HUMAN WELFARE 

fingerlings. The regulation of the fish industry and the pro- 
tection of fish, however, have been left to the initiative of 
the states. Although the protection of fish is primarily a 
state function, the indifference or inability of the states in 
these matters may make federal control desirable if this 
important source of our food supply is to be maintained ; in 
fact, the government has already entered into the protection 
of one of our valuable game fishes in the passage of a law by 
Congress regulating interstate transportation of large-mouth 
and small-mouth black bass. 

To protect adequately the game and food fishes of this 
country a majority of the states have adopted laws or regu- 
lations providing, among other things : (1) safety to the 
fish during the spawning season by prohibiting fishing during 
a part or the whole of that period, or by prohibiting fishing 
altogether over certain spawning areas, in order that the fish 
may reproduce and continue the species ; (2) keeping waters 
inhabited by fish free from all pollutions which are harmful 
to fish life ; (3) preservation of immature fish too small 
for use by regulating, restricting, or prohibiting the devices 
used in taking fish, and by establishing a minimum length 
or weight under which no fish may be caught or possessed ; 
(4) in the case of some game fish, the highest utility of 
which is sport or recreation, eliminating commercialism by 
prohibiting the sale ; (5) using food fish for no purpose 
other than human consumption ; (6) outlawing obstructions 
in rivers and streams that prevent fish from ascending and 
descending for purposes of spawning or in search of food, 
and requiring that fishways be constructed in connection 
with the erection of dams permitting the free passage of fish. 

These laws are enforced principally by State Fish and 
Game Wardens and other state officials ; the necessity for 
regulations covering these general subjects is obvious. 



FISHES AND HUMAN WELFARE 471 

QUESTIONS AND APPLICATIONS 

1. How does a fish differ from all other forms of vertebrates? 

2. Mention six animals commonly spoken of as "fishes " and show why 
each is not a fish. 

3. Name the regions of the body of the yellow perch. State where 
each region begins and where it ends. 

4. Name, locate, and give the number of each kind of fin found on the 
yellow perch. How do the fins of a goldfish differ from those of a perch in 
number and situation ? 

5. How is a perch or a goldfish able to rise or sink by using the air 
bladder? 

6. What part of a fish affords the principal motive power for rapid 
swimming ? What is the use of the tail fin in swimming ? 

7. How are the teeth of carnivorous fishes adapted to catch and hold 
other animals ? 

8. State the situation of the gills of the fish studied. 

9. Describe the three parts of a gill and state the general use of each 
part. 

10. How are the gill filaments adapted by structure for breathing? 

11. How is the goldfish able to get oxygen to the gill filaments and to 
remove carbon dioxid? 

12. What is the most important part of respiration? . 

13. How do the spawning habits of Pacific salmon and common eels 
differ? 

14. Why are fish such an important source of our food supply? In 
what ways are fish preserved until they are eaten? 

15. What kinds of fish are common in your state ? What is the nearest 
fish hatchery? What fish are protected by law in your state? During 
what months is fishing prohibited ? 

16. What fish in the markets are cheapest at this time of year ? Which 
fish are most expensive ? 

17. Give some idea of the value of the salmon fishery ; of the cod fish- 
ery. 

18. In what ways, other than as a source of food, are fish of importance 
to man? 

19. Give an account of the near extermination of the Atlantic salmon. 
Name other fish that are in danger of being caught in too large num- 
bers. 



472 



ANIMALS AND HUMAN WELFARE 



20. Describe each of several steps that should be taken to protect our 
supply of fish. 

21. Which kind of fish in the waters in or about the United States is 
the largest? the smallest? 

22. Why is fishing for trout or bass so much more of a sport than fish- 
ing for flounders? 

23. Find out why a fish cannot live out of water very long at a time. 

24. Which fins of a fish correspond to the arms of a man? 

25. Explain why the two dorsal fins of a perch (111. p. 452) are not 
paired fins. 

26. What is the name of the most important food fish in the world? 

Summary of Classification of Vertebrates 



Class 



Mam- 
mals 

Birds 



Reptiles 



Am- 
phibia 

Fishes 



Examples 



Cows 
Man 

Robins 
Sparrows 



Turtles 
Lizards 



Frogs 
Toads 



Codfish 



Covering 
of Body 



Skin 
with hair 

Skin 

with 

feathers 



Scaly 
skin 



Naked 
skin 



Scaly 
skin 



Warm- 
or Cold- 
blooded ] 



Warm- 
blooded 

Warm- 
blooded 



Cold- 
blooded 



Cold- 
blooded 



Cold- 
blooded 



Appendages 

Used in 
Locomotion 



Paired append, 
with nails 

Anterior ap- 
pend, wings ; 
poster. ap- 
pend, with 
claws 

Two pairs ap- 
pend. Toes 
with claws 

Two pairs ap- 
pend. Toes 
without claws 

Fins and tail 



Organs of 
Respiration 



Lungs 



Lungs 



Lungs through- 
out life 



Gills in tadpole, 
lungs in adult 



Gills 



1 Cold-blooded animals are those animals in which the temperature of the blood 
changes with the temperature of their surroundings. Warm-blooded animals, 
on the other hand, maintain under normal conditions an almost constant tempera- 
ture. The temperature of the human body, for example, is 98.6° F. in the mouth, 
which is usually higher than the temperature of the earth, air, and water ; in con- 
trast, when we touch a fish or frog, the animal feels cold. 



FISHES AND HUMAN WELFARE 



473 






»-o 3-g fe.s 

0><+- .- -r-l 0> 



££>?£ 






>gs "O 



o3 T3 

■§£§33 

jC o S d 1) 






^agi^a 



c3^>> 



01m oo 

a> ra 03 o> to 
. O > o3 

«S *° . - £ 

>~:d c 2 

Sil I- 



fa W fa>g 



1 « 



H z W 



H B * Z* 



fe CO. 2 01 

£ o >— i 

T 2 3"£ 



^ W 3 

88 "S ° 



[J 03. « 0> 



&y$$ 



o o 
. is v 

S3 5 > 
■33 5 

03 S 



£ * <U 
-ft<£ > 



O M 3 



o3 « | 



5^3 P 
O^gft 



X! o3 
nT3 -^> 



T3^ 

P 2- 



2 22,2 

fa 



o ft 

^2 5 



~G 0> 
01 ^ 

o a 



d o> 

SI 

o> c 



Cms 

O Oi ft 



5^ 

o a 



£ « 



£"2 i 
o'S o 



s-s 









2flCo3 

03 03 C3,ft 



*T> 



-a 

^73 



!*3 



g H 



§ 2 



ft5 



?T3 



l|3 
B<33 



5 a 

►a «! 

fa £ 



03. a o 

c^ ft 
— o >>^ 

pq 



™ £ 6 

a B b 

.m -^ a 

N o O 

22S 

►*- . 

03 2 3-3 






£ 2 a 

2 § 

t, C5J3 



M 03 hj 

'sa ffi 

2 S 



pq 



22 
2 



~ o-^ o> 

H 03X2 



Pi * 

C"o3 
2 P 



PQ 



2^ 

H o3 

2? 



pq 



474 ANIMALS AND HUMAN WELFARE 

PROBLEM 6. HOW ARE INSECTS RELATED TO HUMAN 

WELFARE? 

Butterflies and Moths 

EXERCISE 68 

Study of a butterfly. Laboratory study. 

Materials: Mounted butterflies (if possible in glass cases) with 
sucking tubes uncoiled ; live butterflies in cages ; pieces of wings for 
microscopic study. 

A. Regions and appendages: Examine a butterfly and distinguish 
(a) the front, or anterior, region, called the head; (6) the middle region, 
called the thorax; and (c) the hind, or posterior, region, known as the 
abdomen. 

1. Which region is the smallest? Which is the widest? Which 
region is the longest? 

2. To which region are the legs and wings attached? What other 
region has other kinds of appendages ? 

3. Which region seems to have no appendages? 

B. Organs of the head; feeding. 

1. Observe two long, slender appendages attached to the head. 
These are called antennse (an-ten'e, singular antenna). State the 
position of the antennse on the head and describe their shape, stating 
which end is the thicker. 

2. Near the base of the antennas find the eyes. State their position 
on the head, their shape, and their size (as compared with the rest of 
the head). Suggest the advantage to the butterfly of having bulging 
eyes. 

'3. Study a prepared specimen with the sucking tube (proboscis) 
uncoiled, or uncoil the tube in a living or in a relaxed specimen. 
Describe the position and appearance of this feeding organ. 

4. (Demonstration by the teacher.) Dip a dissecting needle in a 
drop of honey or molasses diluted with water, put the needle into the 
coil of the sucking tube of a live butterfly, and gently unroll the 
tube. 

a. Describe what is done. 

b. Watch the size of the drop. What reason do you find for believing 

that the butterfly is feeding? 



INSECTS AND HUMAN WELFARE 475 

C. Organs of the thorax ; locomotion. 

1. How many pairs of wings has the butterfly? 

2. Compare the length and breadth of one of the wings. What can 
you say concerning the thickness of the wings ? 

3. Hold a butterfly between yourself and the light and study care- 
fully the course of the veins in the two wings on one side. Toward 
what part of each wing do the veins converge? How are the veins 
adapted to give support to the rest of the wing? 

4. Take a small piece of the wing of a butterfly and rub the surface 
with your finger tip. 

a. Describe what you have done and compare the color of the sub- 

stance on your finger with the color of the part of the wing 
before it was rubbed. To what therefore is the color of the 
wing due? 

b. Shake some of the powder from a wing upon a glass slide and 

examine it with a low power of the compound microscope.. 
The bodies that you see are scales. At the end is a tiny stem 
by which the scale is attached to the wing, and at the other 
end usually one or more notches. Make a sketch (much 
enlarged) of one or more of the scales of the kind of butterfly 
you are studying. 

5. Examine the legs of a butterfly. (Some butterflies have a tiny 
pair of front legs that are usually folded against the thorax ; so you 
will need to look very carefully before deciding as to the number of 
legs.) 

a. How many pairs of legs has this butterfly? 

b. Are the legs long and slender or short and thick? 

c. Is each leg all in one piece or is it made up of sections with joints ? 

d. Examine the lower end of a leg (foot) and describe what you find. 

Use a magnifier if necessary. How is the butterfly adapted 
for clinging to plants ? Are the legs adapted for rapid crawling 
or running? Give reason. 

6. Make a drawing (natural size) of the upper (dorsal) surface of a 
butterfly and with the sucking tube (proboscis) partly uncoiled. Label 
one of the Antennae, one of the Eyes, Proboscis, Head, Thorax, Abdomen,, 
Wings, and the Veins of one wing. 

A comparison of butterflies and moths. Butterflies and 
moths belong to the same group of insects, which is known 



476 



ANIMALS AND HUMAN WELFARE 



as Lepidoptera (lep'i-dop'ter-a, from the Greek, meaning 
scale-winged), so called because their wings are covered with 
microscopic scales. These scales are attached to the wings 
in the following manner : In the membrane of the wings are 

minute pockets into 
which fit the stems of 
the scales. The latter 
are usually arranged in 
rows and overlap some- 
what like the shingles 
of a roof (111. at left). 
The scales, however, 
are not firmly attached 
since the slightest 
touch is sufficient to 
dislodge many of them. 
When the scales are 
rubbed off, the color of 
the wings and a certain 
amount of their rigid- 
ity disappear. Not 
only are the scales found on the wings, but, in the shape of 
hairs, they form a fuzzy growth over the surface of the rest of 
the body. 

Moths are distinguished from butterflies in the following 
ways : Moths when at rest hold the wings horizontally, while 
butterflies hold them vertically, that is, erect. The wings of 
moths are not usually so brilliantly colored as are those of the 
butterflies. Most moths fly at night while butterflies are day 
flyers. The bodies of moths are usually relatively broader 
than those of butterflies. Moth antennae are of various shapes, 
often like feathers, but never knobbed like those of butterflies. 
Moths in many cases form cocoons ; butterflies never do. 




Courtesy of American Museum of Natural History 

Scales on a butterfly's wing 

How is each scale attached to the membrane of 

the wing ? 



INSECTS AND HUMAN WELFARE 



477 



Reproduction and life history of butterflies and moths. 

The development of the butterfly begins with a special cell 
known as an egg cell. These egg cells are formed in the body 
of the female. When these egg cells have been fertilized 




Spiracle 



Developing icings 



Head 

Mandible 
Spinning tube '' 



Antenna 



Dissected larva Head of larva 

Rearranged from chart by A. Pichler's widow and son 

Cabbage butterfly — eggs and larvae 
How does the caterpillar get out of the egg ? 



by sperm cells from the male butterfly, the eggs are deposited 
on the underside of the leaves of plants on which the young 
can feed. These egg cells divide and subdivide till at last 
a many-celled organism is developed that is often called a 
I worm " but more correctly is known as a caterpillar or 
larva (111. above). 



478 



ANIMALS AND HUMAN WELFARE 




The tiny caterpillar emerges from the covering of the egg 
(that is, it hatches) and begins to feed upon the leaf. As it 
feeds, it grows ; and from time to time it sheds, or molts, 
the more or less hardened skin that covers the whole insect. 
At last after several molts (111. p. 479) the caterpillar reaches 
its full size and then stops eating. At no time in the growth 

of the caterpillar could it be mistaken 

for a butterfly. It has no wings, no 

antennae; and instead of a sucking 

W^JP 1 A W palp tongue, one finds a pair of strong jaws 

with which it eats leaves. The dis- 
tinction between thorax and abdomen 
is not at all clear, and at first sight it 
seems to have more legs than does a 
butterfly. Only the three pairs of 
front legs, however, are jointed, but 
they are so short and thick that there 
seems to be no resemblance between 
them and those of a butterfly. The 
other " legs," found on the abdomen, 
are not jointed structures and hence 
are not really legs at all (111. p. 477). 
The mature caterpillar now attaches itself to some object 
and, after molting once more, usually assumes quite a 
different shape and forms about itself a hardened covering, 
within which a marvelous transformation occurs. The long, 
coiled proboscis appears as a feeding organ (111. above), 
Instead of the jaws, and long, slender, knobbed antennae are 
formed on the head. Two pairs of beautifully colored wings 
develop on the thorax, as do the three pairs of slender, jointed 
legs. At last the fully developed butterfly breaks through 
the covering that incloses it. After the veins of its wings 
are filled with air and the wings are dried, it flies away. 



-Labial 

palp 



^Maxillary 
palp 



Proboscis 



Rearranged from chart by 
A. Pichler's widow and son 

Head of a cabbage butterfly 
Compare with head of a cat- 
erpillar (See 111. p. 477) and 
state what changes have taken 
place in mouth parts. 



INSECTS AND HUMAN WELFARE 



479 



It is evident then that the butterfly passes through four 
fairly distinct stages. First we may distinguish the egg 
stage, then the caterpillar, or larva, stage, and later the 
transformation stage during which it is called a pupa (plural, 




~-'Head^. 



Thorax 



"Silken 
cord 



-Proboscis 



"Spiracles 



Hooks that 

attach pupa 

to support 




Antenna"' %' 



Spiracles 



Formation of pupa 
{shedding larva skin) 



Adult emerging 



Rearranged from chart by A. Pichler's widow and son 

Cabbage butterfly 
Compare with the illustration on page 477 and state what new organs are formed 
during the pupa stage. How is the chrysalis attached ? 

pupce) or chrysalis (kris'd-lis) . At last we have the fully 
developed, or adult, insect that emerges from the pupa 
stage. 

In general the life history of moths is very much the same 
as that of butterflies except that the larvae of many moths 
before assuming the pupa stage spin a more or less silky 



480 



ANIMALS AND HUMAN WELFARE 



covering of threads about themselves as does the silkworm 
caterpillar (111. p. 487). This outside covering of the pupa 
is known as a cocoon. Hence a moth pupa is usually doubly 
protected : first, by the hard shell that forms, like that in 

butterflies ; and, sec- 
ond, by the tough 
silken cocoon. 

What relationship 
butterflies and 
moths have to human 
welfare. The larvae 
of both butterflies 
and moths are vo- 
racious feeders (111. 
p. 481), as anyone 
knows who has had 
any experience with 
caterpillars. In fact 
they may be called 
animated feeding 
machines, since the 
animal in this stage 
must not only pro- 
vide for its own 
growth but must also 
store up enough food 
to form the new 
parts, such as wings 
and legs. The larvae (caterpillars) of many butterflies and 
of some moths are not considered harmful, however, since 
they are not prolific enough to have any serious effect upon 
vegetation, which is the source of food of most caterpillars. 
Indeed, some of the larvae feed on plants that are not useful 




Piwiograyh oy Cornelia Clarke 

Polyphemus moths 
Male above, female below. Note the string of eggs. 



INSECTS AND HUMAN WELFARE 



481 



to man. This is true of the larvae of the monarch, or milk- 
weed butterfly, which feeds on the leaves of the milkweed. 

Most butterflies and 

moths are incapable of 
doing any harm in the 
adult stage since, when 
they eat anything at all, 
they most commonly 
suck the nectar of flow- 
ers. When the flowers 
are visited in this way, 
they are very likely to be 
cross-pollinated and thus 
are benefited instead of 
injured. But in general 
the moths and butterflies 
play but little part in 
the very important proc- 
ess of cross-pollination, 
most of this work being 
done by the bees. The 
following are a few of 
the injurious forms of 
butterfly and moth larvae. 

Cabbage butterfly. 
This is one of the few 
forms of butterfly larvae 
that are of sufficient 
economic importance to 
be worthy of mention. Anyone who has been near a cabbage 
patch may have seen many rather small white butterflies 
hovering about among the cabbages. These are cabbage 
butterflies depositing their eggs on the leaves. The small 




Courtesy of Science Service 



Corn "worm" 

Note the damage done to the corn ears by the 

larvae. 



482 



ANIMALS AND HUMAN WELFARE 



green caterpillars that develop from the eggs very soon show 
what they can do in the way of eating. The ragged appear- 
ance of the young leaves is 
a warning to the gardener 
to " get busy " if he desires 
a crop. The caterpillars 
do most harm when the 
cabbages are young, since 
these plants may be so in- 
jured as to be unable to 
form heads. The cater- 
pillars are often killed by 
being poisoned with arse- 
nate of lead. This may 
be mixed with water and 
sprayed on the young 
plants, or applied as a 
dust. 

Tussock moth. The 
caterpillars of the tussock 
moth attack our shade 
trees. When they are un- 
checked, they will practi- 
cally strip the trees of 
their leaves. The female 
moth is wingless (111. at 
left). When she emerges 
from her cocoon, she lays 
a mass of eggs upon the 
outer surface of the cocoon 
and secretes about the 
eggs a white foamy mass which soon hardens. If this occurs 
in the autumn, the eggs remain during the winter and the 




.Female moth laying 
eggs on cocoon 



Pupa of 
female 




Larva 

Courtesy of U. S. Bureau of Entomology 

Life history of tussock moth 

What marked difference do you note between 

the adult male and female ? 



INSECTS AND HUMAN WELFARE 483 

following spring they hatch out. The young caterpillars 
attack the leaves of the tree where they hatched ; or if the 
cocoon was placed elsewhere, they crawl up the nearest tree 
and start business at once. 

These caterpillars are great travelers, and this is the way 
the tussock moth spreads through a neighborhood since the 




_ . , Courtesy of Caterpillar Tractor Company 

Spraying trees 

female cannot fly. To capture these insects, one may place 
a band of cotton batting around the trunk of each of the 
trees one wishes to protect. The larvae do not usually 
crawl over this but will, if mature, proceed to enter the pupa 
stage beneath the band. All pupae and egg masses should 
be collected and then burned. This is about as much as the 
individual can do. Where a spraying apparatus is availa- 
ble, the trees should be sprayed with lead arsenate to kill the 



484 



ANIMALS AND HUMAN WELFARE 



caterpillars. This caterpillar is rather handsome as cater- 
pillars go, having a bright red head and a series of yellow 
tufts of hair on the dorsal part of the body (111. p. 482). 

Gypsy moth. The gypsy moth (111. below) was brought 
into Massachusetts from Europe in 1869 in connection with 
scientific experiments. Some of these specimens accidentally 

escaped and gradu- 
ally increased until 
the damage to fruit, 
forest, and shade 
trees caused by the 
larvae was so evident 
that property owners 
had to call upon 
the state to aid in 
their extermination. 
Nearly one million 
dollars was expended 
during a period of 
ten years. At the 
end of this time the 
number of the insects 
was so reduced that 
it was impossible to 
convince taxpayers 
of the necessity for 
further appropria- 
tions to complete the 
extermination. Since then the gypsy moths have spread 
over all the New England States and into the adjoining 
states. 

Codling moth. The codling moth, sometimes referred to 
as the apple worm, is the cause of wormy apples. It is 




\Food plant 
Apple tree 



Female 



Life history of the gypsy moth 
What kinds of trees are injured by this moth ? 



INSECTS AND HUMAN WELFARE 



485 



world-wide in its dis- 
tribution, occurring 
wherever apples are 
grown. According to 
the most recent esti- 
mates; the damage 
caused by the codling 
moth in the United 
States amounts to 
$13,500,000 annu- 
ally. It found its 
way to the United 
States in early colo- 
nial times, probably 
in fruit brought by 
the early settlers. 
The various stages of 
the insect are illus- 
trated on this page. 
The insect's impor- 
tance varies in dif- 
ferent localities. In 
hot arid climates, 
three or four genera- 
tions occur each year, 
and the ' ' worms ' ' are 
extremely abundant 
and difficult to con- 
trol. Under cool, 
moist conditions, 
which are unfavor- 
able to activity on 
the part of the moths, 




,. .Jg^ffi^* 


->' ' 












' . ' ' ' . " 






Courtesy of U. S. Bureau of Entomology 

Life history of codling moth 

Top, larva in apple; middle, pupa in cocoon; bot- 
tom, adult codling moth. 



486 



ANIMALS AND HUMAN WELFARE 



there are only one or two generations a year, and the moths 
lay comparatively small numbers of eggs. Under these con- 
ditions, a single spray application properly timed may give 
satisfactory control for the season, whereas with more severe 
infestations, six or eight applications of lead arsenate are 
often inadequate for complete control. Where a great deal 
of spraying is necessary, the growers wash the harvested fruit 
in dilute hydrochloric acid in order to remove the poison 
before the fruit is placed on the market. 

Clothes moths. " The little buff-colored clothes moths 
(111. below) sometimes seen flitting about rooms, attracted to 

lamps at night or dislodged 
from infested garments or 
portieres, are themselves 
harmless enough, for their 
mouth parts are rudimen- 
tary and no food whatever 
is taken in the winged state. 
The destruction occasioned 
by these pests is, therefore, 
limited entirely to the feed- 
ing or larval stage. The 
killing of the moths by the 
aggrieved housekeeper, while usually based on the wrong in- 
ference that they are actually engaged in eating her woolens, 
is, nevertheless, a most valuable proceeding because it checks, 
in so much, the multiplication of the species which is the sole 
duty of the adult insect." 1 

" Clothing which is in daily use is practically never in- 
fested by clothes moths. It is highly important that cloth- 
ing or other fabrics placed in storage should be free from 
moths. To insure this, such clothing should be thoroughly 

1 Circular No. 36, Second Series, United States Department of Agriculture. 




Larva of clothes moth 

Clothes moth 

In which stage is it harmful ? 



INSECTS AND HUMAN WELFARE 



487 



brushed and shaken and hung out of doors in the bright sun 
for several hours before being packed away. If placed in 
trunks or boxes, clothing may be protected from infestation 
by scattering naphthalene flakes through the box or trunk 
at the rate of 1 pound to 10 cubic feet of space. Paradi- 
chlorobenzene (white crystals that may be obtained at a drug 
store) used in the same way will also give complete protection, 




_ . *■•".«« Courtesy of Japan Tourist Bureau 

Life history of silkworm 
Left, caterpillars feeding on mulberry leaves. Right, cocoons, with emerging moths. 

and will kill any larvae or other stages of the insect which may 
have been in the material when it was placed in storage." 1 
Silkworms. One species of moth, the silkworm (111. 
above), is of great value to man. The larva of this insect 
feeds upon the leaves of the mulberry tree, and after reach- 
ing maturity spins a cocoon of silk requiring about three 
days for its completion. After the cocoons are heated in 
ovens to kill the pupae, the silk is reeled off and spun into 

1 From Metcalf and Flint, Destructive and Useful Insects. Used by permission of 
McGraw-Hill Book Company, Inc., publishers. 



488 ANIMALS AND HUMAN WELFARE 

threads. " For many hundreds of years the cultivation of 
the silkworm was confined to Asiatic countries. It seems to 
have been an industry in China as early as 2600 B.C. and was 
not introduced into Europe until 530 a.d. After the latter 
date, the culture rapidly increased, soon became prominent 
in Turkey, Italy, and Greece, and has held its own in those 
countries, becoming of great importance in Italy. . . . 
Japan to-day produces a very considerable proportion of 
the world's supply of raw silk." l Many attempts have been 
made to introduce this industry into the United States, but 
the experiments thus far made have been rather unsuccessful. 

Grasshoppers and Their Relatives 2 
EXERCISE 69 

Study of the grasshopper. Laboratory study. 

A. Regions and appendages. Examine a grasshopper and dis- 
tinguish the three regions of the body ; namely, (a) the front, or 
anterior, region, called the head; (b) the middle region, called the 
thorax; and (c) the hind, or posterior, region, known as the abdomen. 
(The anterior portion of the thorax is covered by a cape or collar.) 

1. State the part of the body in which each region is found. 

2. Which region is the smallest? Which is the widest? Which 
region is the longest? 

3. Which region has legs and wings attached to it ? Which region has 
other kinds of appendages? 

4. Which region is made up of a number of similar rings, or segments? 

B. Organs of the head; feeding. 

1. Note two long, slender feelers on the head; they are known as 
antennae (singular, antenna). State the position of the antennae on 
the head and describe their shape. 

1 From Bailey, Cyclopedia of American Agriculture, III, 640. Used by permission 
of The Macmillan Company, publishers. 

2 Some teachers may choose to begin the study of insects with the grasshopper. 
The authors have, therefore, repeated in italics many of the terms used and defined 
in connection with the study of the butterfly. 









INSECTS AND HUMAN WELFARE 489 

2. Describe the shape and position of the large eyes. State their 
relative size compared to that of the head. 

3. Find the upper lip on the lower anterior part of the head. De- 
scribe its location and shape. 

4. (Demonstration by the teacher.) Raise the upper lip of a large 
grasshopper and find the jaws, or mandibles, beneath it. With a dis- 
secting needle gently pry the jaws a little way apart. Do the jaws 
move from side to side or up and down as ours do ? 

5. Find the lower lip on the under side of the head (i.e. next to the 
thorax). It is divided vertically into two equal parts. Attached to 
either side is a tiny jointed structure called a labial palpus. 

a. Describe the location of the lower lip. 

b. Describe the position and appearance of the labial palpi. 

6. (Demonstration or home work.) Place several grasshoppers in 
a cage or glass jar with moistened leaves of clover, grass, or lettuce. 
If these insects refuse to eat, try others until you find some that will eat. 

a. Describe the movements of the head and also the movements of 

the mouth parts while the grasshopper is eating. 

b. Which mouth parts must do most of the biting of the leaf? 

Give reason. 

C. Organs of the thorax; locomotion. 

1. How many legs has a grasshopper? W T hich pair is the largest? 

2. Make a sketch (X 4) to show the following parts of one of the 
hind legs : (a) the large segment nearest to the thorax — the thigh, or 
femur (fe'mwr) ; (b) the next segment to the femur — the tibia (tlb'i-a) ; 
(c) the part that rests on the ground when the insect walks — the 
foot, or tarsus (tar'sws). Use a magnifier to see the several segments 
in the tarsus, the little claws at the tip end, and a small pad between 
the claws. Label : Femur, Tibia, Tarsus, Segments, Claws, Pad. 

3. Get a grasshopper to climb up a stick or a piece of grass. 

a. Tell what you have done and describe the movements of the 

animal that you have observed. 

b. How is the insect able to cling to the stick? 

4. (Demonstration or home work.) Place a lively grasshopper in a 
clear space on the floor or in a cage. Get it to jump enough to determine 
the following points : 

a. What is the position of the parts of the hind legs when the animal 
is ready to leap? 



490 ANIMALS AND HUMAN WELFARE 

b. What is the position of the parts of the hind legs the instant the 

insect lands? 

c. What does the grasshopper do to get ready for another jump? 

d. What movement throws the insect into the air? Is this move- 

ment made slowly or quickly? 

e. In what respects are the hind legs better fitted for jumping than 

are the other two pairs ? 

5. Move the outer wings of a preserved grasshopper sideways and 

forward at right angles to the body so as to expose the under pair. 

Spread out, or unfold, the under wings. (It is an advantage to mount 

the specimens on cork and pin the wings in the position named above.) 

a. Which pair of wings, judging by extent of surface, is better fitted 

for flying? 

b. How are the outer wings fitted to protect the under wings when 

the animal is not flying ? 

c. Draw ( X 2) the outline of a front wing and of a hind wing and 

sketch in the veins. Label : Front wing, Hind wing, Veins. 

D. Organs of the abdomen; breathing. 

1. (You will observe that each of the rings, or segments, of the abdo- 
men is composed of an upper and an under part.) Make a sketch 
( X 4) of a side view of four or five segments of the abdomen to show 
the structures mentioned above. Label : Segment, Upper part, Lower part. 

2. In each segment, except those at the tip of the abdomen, there 
is a breathing pore on each side. With the aid of a magnifier look for 
these breathing pores near the lower margin of the upper part of each 
segment. When you have found the pores, show them in your 
sketch of the abdominal segments and label : Breathing pores. 

3. Secure an active grasshopper, put it in a live cage, and watch the 
movements of the upper and lower portions of the abdominal segments. 

a. Describe what you have observed. (These movements are used 

in breathing.) 

b. Which movement would cause exhaling of air and which inhaling ? 

Life history of the grasshopper. The male grasshopper 
may easily be distinguished by the rounded tip of the abdo- 
men ; the abdomen of the female has at its posterior extrem- 
ity four movable parts which constitute the egg-laying organ, 
or ovipositor (6'vi-poz'i-ter) (111. p. 491). The eggs are pro- 



INSECTS AND HUMAN WELFARE 



491 



duced within the body of the female insect. Before these 
eggs can develop, however, each must be fertilized by a 
sperm cell produced by the male grasshopper. After the 
process of fertilization has taken place, the female grass- 
hopper (usually in the autumn) burrows a hole in the ground 
with the tip of the abdomen. From twenty to forty small 
banana-shaped eggs are then laid in the bottom of the hole 
(111. at right). In 
the spring each egg 
hatches into a tiny 
grasshopper, which 
much resembles the 
adult, except that it 
has no wings and its 
head is relatively 
large in comparison 
with the rest of the 
animal. The insect 
begins at once to feed 
and grow ; but since 
its whole exterior is 
hard and resistant, 
growth can take place 
only after this outer 
covering has been 
split and the insect has crawled out. The grasshopper then 
forms a new and larger coat. This process is known as molt- 
ing and takes place five or six times during the life history of 
the animal. The wings usually become more fully visible 
at the fourth molt, and at the last molt the adult insect is 
produced (111. above). Hence in the life history of the grass- 
hopper there are three more or less distinct stages : (1) the 
egg, (2) the developing insect, or nymph, and (3) the adult 




Grasshopper laying eggs 
How is the hole in the ground made ? 



492 



ANIMALS AND HUMAN WELFARE 



Upper lip 
{ labrum ) 



Maxillary 
/ palpus 



Maxilla 



grasshopper. This succession of changes in a life history is 
known as metamorphosis (from the Greek, meaning one form 
after another). But, because in the development of the grass- 
hopper these changes are not so striking as those that occur 
in the life history of the butterfly (p. 477), the metamorphosis 
of the grasshopper is said to be incomplete. It is better, how- 
ever, to refer to it as a direct metamorphosis, that of the 
butterfly being known as an indirect metamorphosis. After 
reaching the adult stage and depositing eggs, the adult in- 
sects die. Some kinds of immature grasshoppers survive 

the winter, and these are 
the grasshoppers that are 
seen early in the spring. 
Economic importance 
of grasshoppers. Our 
laboratory study of a 
grasshopper's mouth 
parts and our observa- 
tions of its methods of 
feeding have shown that 
these insects resemble 
caterpillars, first, in hav- 
ing biting mouth parts (111. above) and, second, in being 
voracious eaters. Hence, a large number of grasshoppers in 
a given area means a considerable destruction of plant life. 
Many " plagues of locusts " (for grasshoppers are more cor- 
rectly known as locusts) have been recorded in history. One 
of the first is that recorded in the Bible, which occurred before 
the departure, or " Exodus," of the children of Israel from 
Egypt. " And they [the locusts] did eat every herb of the 
land, and all the fruit of the trees . . . and there remained 
not any green thing in the trees, or in the herbs of the field 
through all the land of Egypt." (Exodus, x. 15.) 



Mandible 
{jaw) " 



Labial 
palpus 




'--=--** Labium 
{lower lip) 



Mouth parts of a cockroach 

These are similar to the mouth parts of a 

grasshopper. 



INSECTS AND HUMAN WELFARE 



493 



During the years 1866-1882 there were several plagues of 
locusts in the grain-producing states of the West, notably 
Kansas and Nebraska. The Rocky Mountain grasshoppers 
during these years migrated in such numbers that the sky 
was darkened during their flight, and the result of their 
devastation was as serious as that described in Exodus. 
According to one authority this species of insect destroyed 
$200,000,000 worth of 
crops in the Western 
States in four years. 
During 1931 the locusts 
(grasshoppers) were es- 
pecially destructive in 
the Rocky Mountain 
states and in Canada. 

Locusts have been 
used as food, and even 
at the present day they 
are commonly eaten by 
the Arabians. In the 
Bible it is related of 
John the Baptist that 
while preaching in the 
wilderness " he did eat of 
locusts and wild honey." 

Relatives of the grasshopper. Other insects that have 
structure, habits, and life history similar to those of the grass- 
hopper are the crickets, cockroaches, katydids, and walking 
sticks. The cockroaches are very fast runners, as anyone 
knows who has tried to catch them, and their bodies are so 
thin that they can easily hide away in narrow cracks. Their 
sharp jaws (111. p. 492) enable them to feed upon dried bread 
and other hard food. Katydids and walking sticks are strik- 




Courtesy of Bell Telephone Laboratories 

Praying mantis 
Photographed on a dial telephone. 



494 



ANIMALS AND HUMAN WELFARE 



ing examples of protective resemblance ; that is, they resemble 
their surroundings in form or color so closely that they may 
secure protection from their enemies by this means. Another 
curious relative of the grasshopper is the praying mantis (111. 
p. 493). 

Bees and Their Relatives 

Characteristics of honeybees. Honeybees and the less 
useful bumblebees are much alike in their general plan 




Worker 



Queen 



Drone 



Courtesy of U. S. Bureau of Entomology 

The three kinds of bees in a hive 
How do they differ as to size and form of abdomen ? 

of structure ; that is, in both kinds of insects the body con- 
sists of a head, thorax, and abdomen, all these parts being 
covered with hair (111. above). There are two large com- 
pound eyes, two antennae bent in the middle like a human 
arm at the elbow, and five slender mouth parts that make 
up the sucking organ. Likewise on the thorax of each of 
these insects there are two pairs of membranous wings and 
three pairs of jointed legs. 

In a colony of honeybees there are both male and female 
bees ; but by far the greatest portion of a bee colony con- 



INSECTS AND HUMAN WELFARE 



495 



Antenna 



Air sac 



sists of a third kind of bee, known as the workers. But one 
fully developed female is ordinarily present, and she is 
known as the queen. It is her sole business to deposit eggs 
in the wax cells of the honeycomb. Queens have been 
known to lay as many as 3000 eggs in a single day. The 
male bees are called drones, and it is their function to pro- 
duce sperm cells for 
fertilizing the eggs of 
the queen. We have 
been emphasizing the 
fact that eggs ordina- 
rily do not develop 
unless they are ferti- 
lized by sperm cells. 
In this respect some 
of the egg cells of bees 
are strikingly differ- 
ent from those of 
most other living 
forms. Queen bees 
lay certain eggs that 
are never fertilized. 
From these unferti- 
lized eggs drones are 
developed. 

To the workers belong most of the nutritive functions 
of the colony. While they are smaller than either the 
queen or the drones, they are by far more numerous, there 
being as many as 50,000 in a good colony in summer. The 
mouth parts are very complicated, five of them working 
together in sucking up the nectar of flowers. In addition 
there is a pair of horny jaws which the worker bees use 
mainly for building the wax comb, the cells of which are 




Courtesy of U. S. Bureau of Entomology 

Internal structure of a honeybee 

How is air distributed to all parts of the body ? What 

is the function of the honey stomach? 



496 



ANIMALS AND HUMAN WELFARE 



used either for egg-laying or for storing honey. On the 
outer side of the tibia of each of the hind legs is a fringe of 

stiff hairs which help to form 



Femur^ 



Tibia-. 

Pollen s"' 
basket 

Pollen 



Tarsus 1 -^ 




Mass of 

pollen in 

pollen 

basket 




Hind legs of a honeybee 
Find out the use of the scissors. 



a pollen-basket. In these 
pollen-baskets the worker 
gathers the masses of pollen 
(111. at left) which one may 
see when the insect is re- 
turning to the hive. 

The life history of the 
honeybee. The eggs of the 
bee are tiny white objects, 
shaped more or less like a 
banana. A single egg is 

placed by the queen mother at the bottom of each cell in 

the parts of the comb used for brood, hence called brood 

comb (111. at right). 

At the end of three 

days the egg hatches 

into a minute foot- 
less grub, or larva 

(111. at right). This 

is fed for the first 

few days on rich 

food produced in 

the stomachs of the 

workers which are 

acting as nurses. 

The grubs are then 

fed with a mixture 

of pollen and honey, 

and at the end of six days after hatching they are supplied 

with enough of this mixture to last during the rest of the 



J?99^ 



Developing- 
/arvae 



Pupa 




food for Queen /arva 

,1 , , 

^Capped 
'.brood ce//s 



Open brood 
ce//s 



Queen ce//s 



Courtesy of U. S. Bureau of Entomology 

Brood comb of honeybee 

Identify each of the four stages. How do queen cells 

differ from the others? 



INSECTS AND HUMAN WELFARE 



497 



larval stage. The cells are then capped over with wax by 
the workers. There the developing bees pass through the 
third, or pupa, stage (111. p. 496). At the end of twelve 
days worker bees bite their way out of their nursery cells and 
take their share in the busy toil of the hive. 




Courtesy of U. S. Bureau of Entomology 

A model apiary 
Note the bees at the entrance of the hive (center) and on the brood-frame. 

Drones normally develop in cells of the comb somewhat 
larger than those required for worker bees. When the col- 
ony wishes to produce a queen, the workers construct a cell 
about as large as the end joint of one's little finger 
(111. p. 496). As soon as the larva is hatched, it is fed on 
predigested food (p. 496) throughout the larval period and 
is never given the undigested pollen mixture that is supplied 
to the grubs of workers and drones. 



498 ANIMALS AND HUMAN WELFARE 

In what ways bees are of importance to man. In our 

study of flowers, we referred frequently to the necessity 
of the visits of honeybees to insure cross-pollination. For 
nearly all practical purposes in the United States, as far 
as man is concerned, the honeybee is sufficient for this 
function, except in the case of the red clover, which requires 
the help of the bumblebee in the pollination of the flower 
in order to produce seed. In years to come we may be 
sure that the most successful farmers and fruit growers 
will make a practice of utilizing bees for cross-pollination 
of their crops. 

It is roughly estimated that the annual production of 
honey and wax in the United States amounts to between 
twenty and thirty millions of dollars. If scientific manage- 
ment were to be introduced more widely, this output could 
be raised considerably without additional investment. 

Some of the relatives of the bees. Wasps and hornets 
belong to the same order of insects as the bees and resemble 
them more or less in structure. Some kinds of wasps build 
paper comb from wood that they chew with their jaws. 
Ants — insects with which every one is familiar — are 
likewise classed with the bees and wasps, and the social 
communities that they form are marvelous in the degree to 
which they carry division of labor. In some ant colonies, 
in addition to the workers, there are soldiers and slaves. 

Mosquitoes and Flies 

The characteristics and the life history of the house mos- 
quitoes. Unlike the insects we have studied thus far, mos- 
quitoes lay their eggs in water that is quiet or stagnant. If 
the weather is warm and if other conditions are favorable, 
the eggs hatch within a day or two into tiny larvae known as 
wrigglers (111. p. 500), from their characteristic motion in 



INSECTS AND HUMAN WELFARE 499 

the water. In this stage the mosquito larva feeds on the 
microscopic plants and animals that abound in the water. 
Growth takes place, and this necessitates frequent molting, 
or the shedding of the relatively tough outer covering, and 
the forming of a new and larger coat. 

The mosquito larva has a well-developed head, a thorax, 
and a jointed, or segmented, abdomen ; but legs and wings 
are wanting. An important characteristic of this stage of 
the insect is the breathing tube that projects from the hind 
end of the abdomen. For while the mosquito larva lives 
in the water, it is obliged to swim to the surface at short 
intervals in order to get its necessary supply of air. It 
then hangs diagonally or horizontally, according to species, 
with the tip of its breathing tube projecting through the 
surface film into the air above (111. p. 500). 

After attaining its full growth as a larva, the mosquito 
enters the third, or pupa, stage. It now ceases to feed and 
no longer breathes through the single tube at the tip of 
the abdomen, but instead through a pair of tubes that 
project from the upper surface of the thorax. The pupae 
are capable of locomotion. If undisturbed, however, they 
are usually found floating at the surface. During the pupa 
stage the insect develops its piercing and sucking mouth 
parts, its long, slender legs, and its gauzy wings. 

At the final molt the mosquito leaves its pupal case in the 
water and flies into the air an adult mosquito. If it is hatched 
during the spring, summer, or early autumn, it usually lives 
two weeks or more. Many of the females, however, that de- 
velop late in the autumn seek out a protected spot in which 
to spend the winter and thus are ready in the spring to per- 
petuate the species by laying eggs in stagnant pools. 

Nor is a large amount of water necessary for the breeding 
of mosquitoes. The following receptacles, if they remain 




CuUx adult Anopheles adult 

Rearranged from U. S. Bureau of Entomology 

Life history of mosquitoes 

Left, house mosquito ; right, malaria mosquito. State differences in the two types in 

each of the four stages. 



INSECTS AND HUMAN WELFARE 501 

undisturbed for about two weeks, often hold enough water 
to provide for complete development of these pests from 
eggs to adults : old tin cans carelessly thrown into the back 
yard ; gutters of roofs that are allowed to remain clogged 
with leaves ; unscreened rain barrels and cisterns. In such 
cases the careless householder is directly responsible for the 
hordes of insects that not only annoy but also may endanger 
the health and lives of his own family and the families of his 
neighbors. 

Mosquito control. In the vicinity of New York there 
are about forty different species of mosquitoes. Since 
nearly all of them feed upon the blood of man and other 
warm-blooded animals, these insects, if they are present 
in any considerable numbers, are pests and cause depre- 
ciation in the value of property. Of even more importance 
is the fact, proved in recent years, that malaria, yellow 
fever, and dengue (den'ga) fever can be transmitted only 
by the aid of mosquitoes. 

Now the discomfort and the suffering due to mosquitoes 
are largely unnecessary, if communities will but take the 
trouble to eradicate the breeding places of these insects. Every 
householder should make sure that he is not allowing mos- 
quitoes to breed near his home. He should clean up his 
own back yard and cover cisterns and open wells with the 
finest-meshed netting. 

Fish, especially goldfish and minnows, and dragon flies 
are also important helps to man, since these animals devour 
great numbers of larvae, pupae, and adult mosquitoes. In 
fact in some communities in the United States a fish 
known as the top minnow has been the main agency in the 
control of mosquito pests in ponds, pools, and streams. 

Since the mosquito, during its development in the water, 
comes frequently to the surface to secure air for breathing, 



502 



ANIMALS AND HUMAN WELFARE 



a thin film of oil spread over the surface of the water of 
swamps and pools in which they are breeding is a sure means 
of killing them. But the oil treatment is at best but a tem- 
porary means of ridding the community of mosquitoes, since 
the oil has to be renewed every two weeks, especially after 
rains, to make sure that a continuous film covers the surface. 
The larvae of the malaria mosquitoes feed at the surface 
of the water (111. p. 500). This habit makes it possible 




Courtesy of Dr. W. E. Britton 

Treatment of mosquito breeding places 
Left, before ditching ; right, same spot after ditching. 

to kill them with Paris green applied as a dust. The dust 
may be scattered with the hand or with power dust guns 
or by means of airplanes. 

Wherever possible, pools and swamps should be filled in. 
If this is impossible on account of expense, as in the case 
of extensive salt marshes, ditches with vertical sides should 
be dug that will connect with water (111. above) that will 
move into the ditches with the high tide, and out with the 
low tide. In the case of fresh-water swamps the ditches 






INSECTS AND HUMAN WELFARE 



503 



should connect with running water, such as creeks and 
rivers. By these methods of ditching, the standing water is 
drained off, the larvae cannot attach themselves to the verti- 
cal banks of the ditch, and fish are given access to and destroy 
such larvae as may begin de- 
veloping. 

Proof that a yellow-fever 
mosquito transmits the 
germs of yellow fever. 1 The 
demonstration that malaria 
can be transmitted only by 
a certain mosquito from one 
human being to another was 
largely the work of the biolo- 
gists of England, France, 
and Italy (pp. 7 and 8). 
The discovery that another 
kind of mosquito (formerly 
called Stegomyia [steg'6- 
mi'ya], but now known as 
Aedes [a-e'dez]) is respon- 
sible for the transmission of 
yellow fever, however, is due 
to the splendid achievements of the Yellow Fever Com- 
mission appointed by President McKinley. In June,, 
1900, the Commission of Four, headed by Dr. Walter Reed 
(111. above), who was the inspiring genius of the Commission,, 
began its epoch-making experiments in the island of Cuba. 
Within six months these men had demonstrated beyond 
a doubt that this plague disease of the tropics and of our 
Southern States could be communicated only through the 




Photograph by U. S. Army Medical Museum 

Major Walter Reed (1851-1902) 
From painting in Walter Reed Hospital. 



1 See "The Conquest of Yellow Fever" by James E. Peabody, American Museum 
of Natural History, New York City, 33 pages, 38 illustrations, 15 cents. 



504 



ANIMALS AND HUMAN WELFARE 



agency of the female Aedes that had been infected with 
the germs of yellow fever. For this reason these mosquitoes 
are known as yellow-fever mosquitoes. 

This Commission, impressed by the mosquito theory first 
suggested by Dr. Carlos Finlay of Havana, at once began 
experiments to demonstrate its truth. One of the members, 

Dr. Jesse Lazear (la-zer') 
(111. at left), permitted a 
mosquito to bite him. A 
few days later he contracted 
the dread disease and from 
it he died. The inscription 
on a tablet erected to his 
memory in a Baltimore hos- 
pital reads as follows : 
" With more than the cour- 
age and devotion of a soldier 
he risked and lost his life to 
show how a fearful pesti- 
lence is communicated and 
how its ravages may be pre- 
vented." 

Dr. Carroll, another mem- 
ber of the Commission, was also stricken with yellow fever 
after having been bitten by a mosquito. These two cases 
were convincing to Dr. Reed, but they could not be pub- 
lished as positive proof to the scientific world because in 
neither case had there been experimental control. Hence, 
further experimentation was necessary. When it became 
known among the troops that subjects were needed for ex- 
perimental purposes, the first to respond was John R. Kis- 
singer (111. p. 505). He, in company with another young 
private, John J. Moran (111. p. 506), also from Ohio, volun- 




Photograph by U. S. Army Medical Museum 

Dr. Jesse Lazear (1866-1900) 



INSECTS AND HUMAN WELFARE 



505 



teered for this service. This they did, in the words of 
Kissinger, " solely in the interest of humanity and in the 
cause of science." Dr. Reed talked the matter over with 
them, explaining fully the danger and the suffering involved 
in the experiments should they be successful. Then, seeing 
that they were determined, he stated that a definite money 
compensation would be made 
them. Both young men de- 
clined to accept it, making, 
indeed, their sole stipulation 
that they should receive no 
pecuniary reward. Where- 
upon Major Reed touched his 
cap, saying respectfully, 
" Gentlemen, I salute you." 
Kissinger, having been bitten 
by mosquitoes infected with 
yellow-fever germs, was the 
first to get yellow fever under 
experimental conditions. " In 
my opinion," says Dr. Reed, 
" this exhibition of moral cour- 
age has never been surpassed 
in the annals of the Army of 
the United States." 

The object of one of the first experiments was to determine 
whether or not yellow fever could be contracted from cloth- 
ing worn by yellow-fever patients. A small building was 
constructed, the windows and doors being carefully screened. 
Into this were brought chests of clothing that had been taken 
from the beds of patients some of whom had died of yellow 
fever. Three brave men, Dr. Robert P. Cooke and two 
privates of the hospital corps named Folk and Jernigan, 




John R. Kissinger (1877- ) 
Photo at time of enlistment in Cuba. 



506 



ANIMALS AND HUMAN WELFARE 



entered the building, unpacked the boxes, and for twenty 
nights stayed in close contact with the soiled clothing. " To 
pass twenty nights in a small ill-ventilated room, with a 
temperature over ninety, in close contact with the most 
loathsome articles of dress and furniture, in an atmosphere 
fetid with their presence, is an act of heroism which ought to 
command our highest admiration and our lasting grati- 
tude." * In spite, however, 
of these unwholesome sur- 
roundings, none of the men 
contracted yellow fever. 
And so it was proved for all 
time that this disease cannot 
be communicated by means 
of anything that comes from 
the bodies of yellow-fever 
patients. 

Dr. Reed now set out to 
prove that the female Aedes 
was the mosquito by which 
the disease was transmitted 
from one person to another. 
A second building of the 
same size as the first was erected. The room was divided 
by a wire screen, and all the doors and windows were screened 
carefully. Into one of the rooms a number of mosquitoes 
that had bitten yellow-fever patients were freed, and a few 
minutes later John Moran entered and allowed these mos- 
quitoes to bite him fifteen times. On Christmas morning, 
1900, at 11 a.m. this brave young man was stricken with 
yellow fever, but he bore the sharp attack without a murmur. 




John J. Moran (1876- ) 
Photo in uniform of World War. 



1 From Kelly, Dr. H. A., Walter Reed and Yellow Fever. Used by permission of 
The Norman Remington Co., publishers. 



[Public— No. 858 — 70th Congress] 

[H. R. 13060] 

An Act To recognize the high public service rendered by Major 
Walter Reed and those associated with him in the discovery of the cause and 
means of transmission of yellow fever. 

Be it enacted by the Senate and House of Representatives of the 
United States of America in Congress assembled, That in special 
recognition of the high public service rendered and disabilities 
contracted in the interest of humanity and science as voluntary 
subjects for the experimentations during the yellow-fever investi- 
gations in Cuba, the Secretary of War be, and he is hereby, 
authorized and directed to publish annually in the Army Register a 
roll of honor on which shall be carried the following names : Walter 
Reed, James Carroll, Jesse W. Lazear, Aristides Agramonte, James 
A. Andrus, John R. Bullard, A. W. Covington, William H. Dean, 
Wallace W. Forbes, Levi E. Folk, Paul Hamann, James F. Han- 
berry, Warren G. Jernegan, John R. Kissinger, John J. Moran, 
William Olsen, Charles G. Sonntag, Clyde L. West, Doctor R. P. 
Cooke, Thomas M. England, James Hildebrand, and Edward 
Weatherwalks, and to define in appropriate language the part which 
each of these persons played in the experimentations during the 
yellow-fever investigations in Cuba; and in further recognition of 
the high public service so rendered by the persons hereinbefore 
named, the Secretary of the Treasury is authorized and directed 
to cause to be struck for each of said persons a gold medal with, 
suitable emblems, devices, and inscriptions, to be determined by 
the Secretary of the Treasury, and to present the same to each of 
said persons as shall be living and posthumously to such repre- 
sentatives of each of such persons as shall have died, as shall be 
designated by the Secretary of the Treasury. For this purpose 
there is hereby authorized to be appropriated the sum of $5,000; 
and there is hereby authorized to be appropriated, out of any money 
in the Treasury not otherwise appropriated, such amounts annually 
as may be necessary in order to pay to the following-named persons 
during the remainder of their natural lives the sum of $125 per 
month, and such amount shall be in lieu of any and all pensions 
authorized by law for the following-named persons: Private Paul 
Hamann; Private John R. Kissinger; Private William Olsen, Hos- 
pital Corps; Private Charles G. Sonntag, Hospital Corps; Private 
Clyde L. West, Hospital Corps; Private James Hildebrand, Hos- 
pital Corps; Private James A. Andrus, Hospital Corps; Mr. John 
R. Bullard ; Doctor Aristides Agramonte ; Private A. W. Covington, 
Twenty-third Battery, Coast Artillery Corps; Private Wallace W. 
Forbes, Hospital Corps; Private Levi E. Folk, Hospital Corps; 
Private James F. Hanberry, Hospital Corps; Doctor R. P. Cooke; 
Private Thomas M. England; Mr. John J. Moran j and the widow 
of Private Edward Weatherwalks. 

Approved, February 28, 1929. 

The yellow-fever bill 
The record of these men appears each year on the honor roll of the U. S. Army. 




508 ANIMALS AND HUMAN WELFARE 

On the other side of the screen were three soldiers who were 
protected from mosquitoes ; and these men remained in perfect 
health. This experiment proved beyond a doubt that yellow 
fever is transmitted by this particular mosquito. Fortu- 
nately none of the other doctors or the soldiers who were 
stricken were called upon, as was Dr. Lazear, to give up 
their lives in Cuba. Many of those who were experimented 
upon, however, paid the price of early death or long sickness 
after the experiments were over. 

The order with the significance of the crucial experiments 
tried in Cuba was this : Kissinger's case established once 
and for all that yellow fever is conveyed by the bite of a mos- 
quito. Moran's case proved that the mosquito in question 
is Aedes (formerly known as Stegomyia). The experiment 
of Dr. Cooke and others with the infected clothing demon- 
strated that yellow fever is not conveyed, as was formerly 
believed, by emanations that come from the bodies of 
yellow-fever patients. In the course of these investigations, 
as well as afterward, Dr. L. O. Howard, former Chief of the 
U. S. Bureau of Entomology, did much to 
-/Hairs on establish the facts concerning transmission 
of disease by insects, and to arouse people 
Hook to combat these carriers of disease. 

The house fly and human welfare. 
Scientists have proved that the common 
Foot of the fly house fly, also, is undoubtedly the carrier 
How is it adapted to of disease germs. Especially is this true 
carry bacteria? ^ ^ transmission of typhoid fever and 
the intestinal diseases to which the deaths of so many 
young children are due. Practically all parts of the body 
of the fly are covered with hairs. Each foot also has pads 
(111. above) which enable the fly to cling to the walls and 
ceilings. 




INSECTS AND HUMAN WELFARE 



509 



In the adult stage flies feed upon filth of all sorts ; and 
if they alight on the excretions from the intestines and kid- 
neys of typhoid patients, they are almost sure to carry on 
their feet and mouth parts the typhoid bacteria ; then when 
flies come into the house, they may infect exposed milk and 
other foods with these germs. Flies may also carry germs 
of other diseases, such as cholera and tuberculosis. 

The most common breeding places of house flies are in 
piles of horse manure, garbage, and other decaying vegetable 
material. Here the 
female fly lays about 
120 eggs (111. at right), 
which hatch into tiny 
white, legless grubs. 
These feed upon the 
manure or other filth 
and grow rapidly. 
The larva now changes 
into a pupa and then 
the adult fly emerges from the brown pupa case. This life 
history like that of the mosquito requires about two weeks. 
Egg laying begins almost at once, and, since each adult 
female lays about 120 eggs, it has been estimated that a 
single fly through the several generations of a single season 
might have descendants numbering more than twice the total 
human population of the earth, if each fly were to deposit 
but one batch of eggs and all the descendants were to sur- 
vive. In reality, however, a fly usually lays four batches in 
a season ! Hence it is very important to catch and kill flies 
at the very beginning of each season. Because of the danger 
of disease transmission and because house flies are filthy in 
their habits, every housekeeper should seek to eliminate all 
breeding places of flies, keep food covered, kill the few flies 




Life history of the house fly 



510 ANIMALS AND HUMAN WELFARE 

that remain, and so keep them away from the food, for one 
never knows where flies have been crawling or what disease 
germs may be clinging to their bodies. 

City authorities should see that all street refuse and gar- 
bage are removed regularly twice a week or, better, every day. 
All persons responsible for horse stables should make sure 
that the manure either is removed each day or else is packed 
into tightly covered receptacles and then removed at least 
twice a week. To make sure that house flies do not breed 
in the manure on farms, it should be scattered on the fields 
at intervals not to exceed three days, or if kept in piles, it 
should be treated with borax or hellebore. If these various 
suggestions are followed, even farmhouses may be rendered 
practically free from the filthy and dangerous house fly. 

Flies in the treatment of disease. The recent use by the 
late Dr. W. S. Baer and others of blowfly maggots in the 
treatment of certain diseases, especially infected bone (osteo- 
myelitis, ds'te-o-mi'e-li'tis), is a unique method of turning 
a destructive force to the benefit of mankind. Following a 
radical surgical operation the young fly larvae, which are 
raised under sterile conditions, are introduced into the 
wound. As they become grown, they are removed and others 
are introduced. The larvae act as scavengers and rapidly 
remove the diseased tissues and thus check the infection. 
Healing proceeds with marked rapidity under this treatment, 
which is being used extensively in hospitals throughout the 
country. The U. S. Bureau of Entomology has developed 
methods of rearing sterile larvae in large quantities and has 
determined how the healing effects are produced. 

Functions of Insects 

How insects accomplish locomotion. Anyone who has 
tried to catch a fly, grasshopper, or other insect knows that 



INSECTS AND HUMAN WELFARE 511 

these animals develop astonishing speed in flying or jumping. 
The wing of an insect is composed of a thin membrane which 
is made more or less rigid by thickened, tubular structures 
that branch out from the thorax region. These are known 
as the veins of the wing, though they contain air instead of 
blood. If we watch an insect (e.g. a butterfly) when it is 
flying, we note downward and upward movements of the 
wings. Since the weight of the animal and the upward 
stroke of the wings against the air would tend to drive the 
animal downward, it is evident that, in order to keep at a 
given level or to rise in the air, more force must be used in 
the downward than in the upward stroke. If the insect is 
to move forward, the wings must not only strike downward 
but also backward. 

Some insects, like the butterfly and the moth, have a 
relatively large expanse of wings, and therefore a relatively 
slow wing movement only is necessary in flight. Bees and 
flies, however, have comparatively small wings. These 
wings are moved so fast that they may become invisible. 
Since in these wing movements a musical note is produced, 
scientists have been able to compute the rate of vibration by 
comparing the sound produced with that on the musical 
scale. By the use of tuning forks it has been found that in 
male mosquitoes this rate of wing vibration is as high as 880 
per second ; in the female it is 480 per second. 

All insects can move from place to place by using their 
three pairs of legs in walking, crawling, or jumping. In 
many cases the feet are provided with hooks or pads that 
enable the animal to cling to some object for support, or in 
some cases (e.g. the house fly, 111. p. 508) to climb a smooth 
surface that is vertical or even to walk upside down. 

Grasshoppers in addition to their wings are provided 
with other and very effective organs of locomotion. In 



512 ANIMALS AND HUMAN WELFARE 

fact they derive their name from the extraordinary feats 
of jumping which they accomplish largely by their long and 
muscular hind legs. If a boy could jump twenty times 
the length of his legs, that is, a distance of fifty feet from a 
standing position, he would make an athletic record cor- 
responding to that of the common red-legged locust. For 
the hind legs of an ordinary specimen of this insect are about 
two inches long and they frequently leap four feet. A flea, 
in proportion to its size, can jump even farther. 

Breathing and release of energy in insects. If we watch 
a grasshopper or a bee, we may observe that the abdomen 
alternately expands and contracts ; and because of the sim- 
ilarity of these movements to those that take place in our 
own chest region, we are quite right in concluding that these 
movements have to do with breathing. Now why must an 
insect breathe? In carrying on locomotion it is evident 
that coDsiderable energy must be liberated and used. So 
far as we know, this, like other activities of the body, is 
possible only as a result of the process of oxidation. Hence, 
the insect must be liberally supplied with oxygen ; and as 
a result of this process of oxidation, the carbon dioxid 
produced must be given off from the body. 

In our own bodies air is taken in through the nostrils and 
carried to the lungs, and the waste carbon dioxid is given 
off through the same passages. In an insect the openings 
for this purpose are not found on the head, as in our bodies, 
but along the sides of the body, a pair of breathing pores 
(spiracles, spir'd-k'lz) being found on either side of most of 
the segments of the thorax and abdomen (111. p. 491). 
Each breathing pore leads into a tiny tube, which connects 
with the tubes from other pores, and these breathing tubes 
extend to all parts of the body and even out into the veins 
of the wings. In this way all parts of the insect are supplied 



INSECTS AND HUMAN WELFARE 513 

with oxygen, and from all parts of the body carbon dioxid 
is removed. Hence, as in the human body, oxygen and car- 
bon dioxid are carried in a definite system of tubes, but these 
tubes carry gases only and not blood as in the human body. 

A segment of the abdomen of an insect consists of an upper 
portion and a lower portion connected by a flexible mem- 
brane. When the lower part of each segment is moved up- 
wards, the size of the abdomen is decreased and so pressure is 
exerted on the air tubes. In consequence, air with its waste 
carbon dioxid is forced out through the breathing pores. 

Like the air tubes in our own lungs, the breathing tubes are 
composed of elastic material. The tubes, therefore, resume 
their former size after pressure is removed. Hence, when the 
under side of the abdominal segments is moved downward, 
the elastic tubes enlarge, air rushes into the breathing pores, 
and so oxygen is supplied to all parts of the body. 

How insects secure their food. In general, insects may 
be divided into two groups : those that eat solid food and 
those that suck up liquid food. One of 
the marked characteristics of butterflies 
and moths is the long sucking tube. 
Through this hollow structure these in- 
sects draw up the nectar or other liquid 
on which they feed. When the sucking 
tube is not in use, it is rolled into a tight 

coil beneath the head and so is out of the 

Bedbug 
way when these insects move from place 

to place. Bees also secure nectar by a sucking tube which 

is more complicated in structure than that just described. 

The mouth parts of mosquitoes and of bugs (e.g. bedbugs 

[111. above], body lice, and plant lice) are also adapted for 

sucking liquid food. But since these insects live on the 

blood of animals or the juices of plants, their mouth parts 




514 ANIMALS AND HUMAN WELFARE 

are fitted also for piercing through the outer skin of animals 
or the epidermis of plants (111. pp. 7, 500). 

Insects, such as grasshoppers, beetles, and caterpillars of 
moths and butterflies, since they feed on solid food, have 
biting mouth parts, which consist principally of a pair of 
hard jaws with sharp cutting surfaces (111. p. 492). These 
jaws move from side to side rather than up and down. 
Upper and lower lips are also present. 

Insects and Man 

Insects as enemies of man. " The struggle between 
man and insects began long before the dawn of civilization, 
has continued without cessation to the present time, and 
will continue, no doubt, as long as the human race endures. 
It is due to the fact that both men and certain insect species 
constantly want the same things at the same time. . . . 
We commonly think of ourselves as the lords and con- 
querors of nature, but insects had thoroughly mastered the 
world and taken full possession of it long before man began 
the attempt. . . . They have disputed every step of our 
invasion of their original domain so persistently and so suc- 
cessfully that we can even yet scarcely flatter ourselves that 
we have gained any important advantage over them. . . . 
Wherever their interests and ours are diametrically opposed, 
the war still goes on and on, and neither side can claim a 
final victory. . . . Since the world began we have never 
yet exterminated — we probably never shall exterminate 
— so much as a single insect species." * 

" If human beings are to continue to exist, they must 
first gain mastery over insects. . . . Insects in this coun- 
try continually nullify the labor of one million men. . . . 

1 From Metcalf and Flint, Destructive and Useful Insects. Used by permission of 
McGraw-Hill Book Company, Inc., publishers. 




<y W\ si -""^ «* 



^ms^;^- 



516 



ANIMALS AND HUMAN WELFARE 



Insects are better equipped to occupy the earth than are 
humans, having been on the earth for fifty million years, 
while the human race is but five hundred thousand years 
old." i 

Classification of Insects 

The general characteristics of insects. If one were to 
make a collection of insects (111. p. 515), one would find 
that all these animals resemble each other in the following 




Photograph by Cornelia Clarke 

A swallow-tail butterfly securing nectar 

respects : (1) Their bodies are divided into three distinct 
regions, head, thorax, and abdomen ; (2) the head bears 
two antennae and a pair of large eyes ; (3) the thorax has 
three pairs of legs and usually one or two pairs of wings ; 
and (4) the abdomen is composed of a number of rings, or 
segments. Most insects, too, in their life history pass 
through a number of stages that are quite different in appear- 
ance. This succession of forms is known as a metamorphosis 

1 From Howard, L. O., The Insect Menace, 1931. Used by permission of The 
Century Co., publishers. 



INSECTS AND HUMAN WELFARE 



517 



and is particularly noticeable in the life history of butterflies 
and moths, of flies and mosquitoes, and of bees and beetles 
— all of which have four distinct stages ; namely, egg, larva, 
pupa, and adult. 

The orders of insects. In the preceding section we have 
stated some of the common characteristics of insects. Let us 
now consider some of the 
differences in the struc- 
ture of various kinds of 
insects. It must be evi- 
dent to you that a butter- 
fly, a grasshopper, a bee, 
and a mosquito are quite 
different in appearance. 
Biologists have made use 
of these differences in 
structure among insects 
to divide them into groups 
known as orders. If the 
structure of the wings and 
mouth parts of certain in- 
sects are similar, and if 
they pass through the 
same kind of metamor- 
phosis, they are placed in 
the same order. 

Lepidoptera. The but- 
terflies and moths (111. p. 515) are certainly more like each 
other than they are like any of the other insects we have 
studied. The scaly wings (111. p. 476) form the most dis- 
tinctive characteristic of these insects, since no other insects 
are so constructed. In the adult stage, their mouth parts are 
fitted for sucking only, and they pass through four distinct 




Photograph by Cornelia Clarke 

Sphinx moth on bark of a tree 
A striking example of " protective resem- 
blance." 



518 



ANIMALS AND HUMAN WELFARE 



stages in their life history (egg, larva, pupa, adult). The 
metamorphosis is indirect. 

Orthoptera. Grasshoppers (111. p. 491), katydids, crickets, 
cockroaches, walking sticks, and praying mantises (111. p. 493) 




Adult - 



Life history of potato beetle 

belong in the order Orthoptera (or-thop'ter-d), from the Greek, 
meaning straight wings. The hind wings of these insects fold up 
like a fan when at rest, so that the main veins are nearly paral- 
lel to each other, thus suggesting the term "straight wings." 
The front pair of wings are thickened, as in the grasshopper, 





Cotton-boll weevil 
Left, adult beetle ; right, cotton boll infested by larvae. 



INSECTS AND HUMAN WELFARE 



519 



and serve as a protecting cover for the hind pair. The mouth 
parts are fitted for biting. The metamorphosis is direct. 

Diptera. The flies (111. p. 515), mosquitoes (111. p. 500), 
and gnats are classified under the order of Diptera (dip'ter-d), 
from the Greek, 
meaning two wings, 
since all these in- 
sects have only two 
membranous wings. 
The mouth parts are 
usually adapted for 
piercing and suck- 
ing. The house fly, 
however, can only 
suck up liquid food 
or food which it has 
made a liquid. The 
metamorphosis is 
indirect. 

Hymenoptera. 
This order of insects 
includes all the bees 
(111. p. 494), wasps, 
and ants. They 
have two pairs of 
wings, each of which 
has so few veins that 
they look like mem- 
branes, hence the 
name Hymenoptera (hi 'men-op 'ter-d), from the Greek, mean- 
ing membrane winged. These insects have indirect meta- 
morphosis. Their mouth parts in the adult stage are 
adapted for biting and sucking. 




Japanese beetle 

Which stages live beneath the ground ? What parts 

of the plant are the beetles attacking? 



520 



ANIMALS AND HUMAN WELFARE 




Carpet beetle 



Larva of 
carpet beetle 



Carpet beetle 



Coleoptera. This order includes hundreds of thousands 

of kinds of insects. Some of them are destructive forms like 

the potato beetle (111. p. 518), the 
cotton-boll weevil (111. p. 518), 
and the Japanese beetle (111. 
p. 519). All the Coleoptera 
(kol'e-op'ter-d) have an indirect 
metamorphosis. Their mouth 
parts are adapted for biting in 
both the larva and adult stages. 
The characteristic of the beetles 
that will enable one to dis- 
tinguish an adult beetle from 
any other kind of insect may 

readily be determined by examining the front wings of one of 

these insects, for the front 

pair of wings is hard and 

horny. When the hind 

wings are folded, the hard 

front pair completely covers 

the delicate membranous 

hind pair. Hence the 

name given the beetles is 

Coleoptera, from the Greek, 

meaning sheath-winged. 
Insect families, genera, 

and species. Each of the 

orders of insects has been 

divided by biologists into 

still smaller groups of in- 
sects known as families. 

Thus we have the swallow-tail family of butterflies and the 

mosquito family of diptera. 




Courtesy of Science Service 

Plum curculio 
Adult beetles on young peach fruit. 



INSECTS AND HUMAN WELFARE 521 

Again, the families are still further divided into genera. 
We have, for instance, the genera, Culex (house mosquito), 
Anopheles (malaria mosquito) (111. p. 500), and Aedes (yel- 
low-fever mosquito). Lastly, the genera are divided into 
species in which the insects are very nearly alike in all 
respects. Thus the family of diptera, to which the house 
fly belongs, is known as Muscidce (mus'i-de), the genus as 
Musca, and the species as domestica. Hence the house fly 
is known scientifically as Musca domestica (111. p. 509). 

QUESTIONS AND APPLICATIONS 

1. In your notebook write in vertical columns the numbers in order 
given below. Write the word or words to complete accurately the unfin- 
ished statements. 

The adult butterfly or moth feeds by means of (1), and the larvae by 
means of (2). The larva? of flies are called (3), and the larvae of mos- 
quitoes are called (4), and the larvae of moths and butterflies are called (5). 
The tussock moth injures (6). Typhoid-fever germs are often carried to 
the food of people by (7). The Colorado beetle injures (8). Butterflies 
cling to flowers by means of (9). The kind of insect that injures ears of 
corn is the (10). 

2. If the italicized words in the statements below make true state- 
ments, write T after the appropriate number. If the statement is false, 
write F, and supply the right word or words. 

The jaws of the grasshopper move up and down (11). Most house flies 
lay eggs in stagnant water (12). The codling moth injures apples (13). 
The Aedes mosquito transmits the germs of typhoid fever (14). The 
breathing organisms of insects are called lungs (15). The grasshopper 
exhales air by making the abdomen smaller (16). The silkworm moth 
spins silk in the adult stage (17). Some moths form cocoons (18). The 
bumblebee is needed to cross-pollinate red clover blosso?ns (19). The cater- 
pillar has more than three pairs of jointed legs (20). 

3. In the following multiple- or alternate-choice statements write the 
correct statement after the number. 

The insects that are most useful in cross-pollinating fruit-tree blossoms 
are (a) bumblebees; (b) moths; (c) flies; (d) honey bees (21). The 
most effective method of controlling mosquitoes is (a) oil on water; 



522 ANIMALS AND HUMAN WELFARE 

(b) ditching; (c) filling in; (d) " swatting" (22). The most effective 
method of house-fly control is to (a) " swat" the fly; (6) drain stagnant 
pools ; (c) treat manure piles with borax (23). An insect that does great 
harm to the cotton is the (a) grasshopper; (6) army worm; (c) boll 
weevil; (d) Colorado beetle (24). An insect that has direct meta- 
morphosis is the (a) butterfly; (6) beetle; (c) house fly; (d) grass- 
hopper (25). 

PROBLEM 7. HOW ARE CRUSTACEA RELATED TO 
HUMAN WELFARE? 

Habits of crayfish. Crayfish are found commonly 
throughout the United States in rivers and their tributaries 
where limestone is found, since lime is needed in making their 
hard outer covering. During the day they hide under 
stones, in the crevices of rocks, in the mud, and sometimes in 
specially constructed burrows along the banks. Since the 
animal backs into these hiding places, its big claws are ready 
for business if an enemy attacks it. 

Then, too, the colors of crayfish aid somewhat in protect- 
ing them, since these colors are usually similar to the color 
of the bottoms of the streams in which they live. Lastly, 
the wide range of vision which the stalked eyes afford must 
serve to warn the animal of the approach of danger. Never- 
theless they do not always escape, since crayfish are often 
captured by certain birds and fishes. In fact, crayfish are 
often used by man as a bait for catching fishes. 

EXERCISE 70 
The structure and functions of a crayfish. Laboratory study. 

A. Regions. The body of the crayfish has only two distinct 
regions. The dorsal surface and sides of the anterior region are 
covered by a cape, consisting of a single piece of shell-like material. 
This region is the cephalothorax (sef'a-16-tho'raks, from the Greek, 
meaning head-thorax). The posterior region is the abdomen. 



CRUSTACEA AND HUMAN WELFARE 523 

1. Which region is composed of a number of similar segments? 

2. Which region has the legs, antennae (feelers), and eyes attached 
to it? 

B. Adaptations for walking. Place a crayfish in the center of a pan 
with enough water to cover the animal. If the crayfish does not walk, 
touch it with the pincers. 

1. How many pairs of legs are used in walking? 

2. In what directions (forward, backward, or sideways) are you able 
to get the crayfish to walk? 

3. State whether or not the " large claws " are used in walking. 

4. Are the walking legs composed of one piece or of several movable 
parts ? Of what advantage is this arrangement to the animal ? 

C. Adaptations for swimming. Place an active crayfish in a pan 
nearly filled with water. Use the following means to get it to swim : 
Make a sudden movement toward it with the forceps or pencil ; if this 
does not succeed, take hold of the animal near the anterior end where 
you can press the large pincers against the body. Do this quickly 
and release the animal. This action may cause the crayfish to swim 
in order to escape. If you cannot get this crayfish to swim, try 
another. 

1. In what direction does the crayfish swim? 

2. State whether or not the legs are used in swimming. 

3. Watch the segments of the abdomen and the large appendages at 
the posterior end to determine their action in swimming. 

a. Describe the direction of the movements of these parts. 

b. Are these movements made slowly or quickly? 

4. In what direction will the doubling under of the abdomen tend to 
send the animal? 

5. In what direction will the straightening out of the abdomen tend 
to send the animal? 

6. In what direction, therefore, must the crayfish strike the harder 
and more quickly in order to swim backwards ? 

D. Adaptations for breathing. 

To the teacher. Prepare some freshly killed or preserved crayfish in the following 
manner : Insert the point of the scissors beneath the posterior margin of the cape 
that covers the cephalothorax and halfway between the middle line of the dorsal 
surface and the lower margin of the cape ; cut forward to the front end of the cape 
and remove the piece of shell. 



524 ANIMALS AND HUMAN WELFARE 

1. Immerse in water a crayfish prepared as directed above. Ex- 
amine and describe the structures that you find above the legs on the 
side where the cape has been partially removed. These structures 
are the special breathing organs of the crayfish. They are known as 
gills. 

2. Push the gills to one side and find the soft body wall. Higher 
up find the line of attachment between the shell and the body wall. 
You will see that the gills are not inside the body, but in a space 
between the body of the animal and its shell. This space is called the 
gill chamber. 

a. In what region of the crayfish are the gill chambers found ? 

b. What forms the outer wall of each gill chamber? What forms 

the inner wall? 

c. Lift up the cape on the opposite side of the animal ; state where 

it is free from the body wall. 

3. Examine the gills on a leg that has been removed from the thorax 
and floated on water and note that it is largely composed of numerous 
slender divisions called gill filaments. 

Make a sketch of the leg ( X 2) with the gills attached. Label Leg 
and Gill filaments. 

4. The gills are furnished with numerous minute thin-walled blood 
vessels and the blood in them is separated from the water only by a 
thin membrane. The blood flows into the gills from all parts of the 
body by one set of blood vessels and leaves the gills by another. 
Bearing in mind that breathing is essentially the same in all living 
things, state : 

a. What gas will the blood bring from the body to be given off in 

the gills in the process of respiration ? 

b. What gas is taken up by the blood in the gills to be carried around 

the body? 

c. How are the gill filaments fitted by structure to permit this inter- 

change of gases? 

d. How are the delicate gill filaments protected from injury? 

5. If the same water remained on the gills for some time, what 
changes in the amount of oxygen and carbon dioxid in the water next 
to the gills would occur? Why, then, is it necessary that a current of 
water should pass over the gills ? 

6. Do currents of water pass through the gill chamber? (Demon- 
stration.) Inject by means of a pipette some harmless coloring matter, 






CRUSTACEA AND HUMAN WELFARE 525 

such as powdered carmine in water, into the posterior end of the gill 
chamber. Place the crayfish again in water. 

a. State what is done in this experiment. 

b. Give your observations and conclusion. 

c. What gas will an incoming current of water bring to the gill 

filaments ? 

d. What gas will a current of water carry away from the gill fila- 

ments? 

7. How the crayfish causes a current of water to pass through the 
gill chambers. 

To the teacher. Prepare several living crayfish so that the action of the gill 
bailer may be seen. To do this, carefully cut off with scissors a small part of the 
anterior portion of the shell just over the gill bailer. 

Watch the movements of the small bladelike body in front of the 
gill chamber. This body is the gill bailer. 

a. Describe the movements of the gill bailer. 

b. When it moves upward and forward, what effect will the gill 

bailer have on the water in front of it and in the gill chamber? 

c. Where can water enter the gill chamber? (See D, 2, c.) 

E. Adaptations for protection. 

1. Describe the outer covering of the crayfish. Of what use is this 
to the animal? 

2. Locate the softer parts of the crayfish's armor. How are these 
protected by their position ? 

3. Gently touch the eye of a living crayfish. Describe the move- 
ments of the eye. How might the movements of these eyes on stalks 
be advantageous to the animal? 

4. Notice the large " feelers " (antennse). What movements do 
you notice? How might these feelers be advantageous to the animal? 

5. Of what use may the large pincers be in addition to helping in 
securing food? Sketch one of the large pincers complete and label it. 

F. Additional drawings. 

1. Identify the parts of one of the large antennse. Notice the 
broad finlike part at the base of the antenna, then two segments, and a 
long lash that arises from the second segment. Sketch (X 2) a large 
antenna. Label. 

2. Make a sketch of the dorsal view of the crayfish. Label the 
regions and all the appendages. 



526 



ANIMALS AND HUMAN WELFARE 



Food, food getting, and digestion. At night crayfish 
crawl about in search of food, about which they are not at all 
fastidious, since fish and other animals seem to be fully as 
acceptable when dead as when alive. In fact, they are nat- 
ural scavengers. Crayfish seize their food with their large 
claws and with the aid of the small pincers (111. below) on the 
front walking legs and with the mouth parts, especially the 



^Antenna 



•Heart 

/Sperm art/ 
/Sperm duct 

/Dorsai diood vesse/ 
-Intestine 



Eye*' 




"Nervous system 
Ventral b/ood vesse/ 



Zarye p/ncer "^Sma// pincers 

Internal organs of a crayfish 
Point out the organs used in locomotion. Name the parts of the alimentary canal. 
Where is the nervous system located ? 

jaws or mandibles, reduce the food to pieces small enough to 
be eaten. Crayfish, like the higher animals and man, have 
a digestive system, which is devoted to preparing the food 
for absorption and use. This system includes the alimentary 
canal which consists of gullet, stomach, and intestine, and 
certain digestive glands. 

After the food is digested, it can pass into the blood by 
osmosis and be carried to the cells of the body. When the 






Antenna Stalked eye 



Gill bailer — * 
Mouth parts -c 




CRUSTACEA AND HUMAN WELFARE 527 

digested food reaches the cells, it may be used by the proto- 
plasm either in making more living matter or, as we shall 
now see, for the release of energy. 

Respiration and the production of energy. In our lab- 
oratory study we watched the movements of the gill bailer 
and saw that it caused a current of water to enter the pos- 
terior end of the gill 
chamber and flow 
over the gills, thus 
bringing oxygen to 
the filaments (111. 
at right) . The thin- 
walled blood vessels ^ s ^^^^^^^M^' ( ^'^'^--\ Gills 
in the filaments ab- Breathing organs of a crayfish 
SOrb the Oxygen, and To what is each gill attached? How are the gills 

the blood then passes protected ? 

on into other blood vessels, which carry it back to the heart, 
whence it is forced all over the body of the crayfish, and so 
the oxygen in the blood passes into the cells as does the 
food. Now what becomes of the oxygen within the animal? 

As in man and other animals, the oxygen unites with 
elements in the foods or protoplasm of the cells and produces 
oxidation and liberation of energy, which gives the crayfish 
the power to contract its muscles and so push against the 
water with its abdomen and tail fin, thus propelling the 
animal backward ; or to open its nippers and shut them and 
so secure food. In fact, all the work that the crayfish per- 
forms is made possible through the oxidation of its foods or 
protoplasm. 

Since the proteins, fats, carbohydrates, and protoplasm 
all contain carbon, when these are oxidized, carbon dioxid 
will be formed as one of the waste substances. All these 
waste substances will pass out of the cells into the blood, 



528 



ANIMALS AND HUMAN WELFARE 



which finally conveys them to the filaments of the gills. 
Here the carbon dioxid passes out into the water, which is 
then forced out of the front end of the gill chamber. 

Life history. Crayfish like other many-celled animals 
are reproduced by means of egg cells which in crayfish are 
formed in the body of the female in ovaries. Before they 
can develop, however, these egg cells must be fertilized by 
sperm cells, produced in spermaries of the crayfish (111. 

p. 526). After the 
eggs are fertilized by 
sperm cells from the 
male crayfish, and 
are forced out of the 
body of the female 
through the egg- 
tubes, they are at- 
tached by a sticky 
substance to small 
appendages, or swim- 
merets, on the ventral 
surface of the ab- 
domen of the female. 
Here the fertilized 
egg cell develops 
into a many-celled embryo, and finally a tiny crayfish hatches. 
At first the young crayfish are held to the swimmerets by 
threads ; later they cling by means of their pincers, and after 
some days become independent. At intervals in both young 
and old crayfish, the hard outer covering of the body is 
molted. Without this process it would be impossible for the 
young to grow. 

While the young crayfish are attached to the parent, they 
are, of course, protected by their position, and the female 




Courtesy of American Museum of Natural History 

A lobster catching a crab 
Note seaweeds of different types. 



CRUSTACEA AND HUMAN WELFARE 529 

looks after them by looking out for herself. The food for the 
developing embryo is stored in the egg. After hatching, the 
young must care for themselves, for they receive no protec- 
tion at all. There is, therefore, in the case of crayfish noth- 
ing like the parental care of higher animals. 

Relatives of the crayfish. One of the relatives of the cray- 
fish is the lobster (111. p. 528), which is a salt-water animal 
found along the North Atlantic coast. Like that of the 




Courtesy of American Museum of Natural History 

Hermit crabs in mollusk shells 

crayfish, its body consists of a cephalothorax and a clearly 
segmented abdomen. The lobster also has two pairs of 
antennae, a pair of stalked eyes, a number of pairs of mouth 
parts, a pair of big claws, four pairs of walking legs, to the 
bases of which gills are attached, and a pair of swimmerets 
on each of the segments of the abdomen except the last. 
In general, lobsters are very much larger than crayfish, one 
of the largest known specimens weighing over forty-seven 
pounds. 

Less like the crayfish in appearance are the crabs (111. 
p. 528), yet a careful examination shows that these animals 
have practically all of the characteristics mentioned in the 




530 ANIMALS AND HUMAN WELFARE 

preceding paragraph. The cephalothorax of crabs, however, 
is usually wider than it is long, and the abdomen is much re- 
duced and is commonly folded in a groove beneath the cepha- 
lothorax. Few of the crabs are able to swim ; usually they 
crawl sideways by the help of their four pairs of 
walking legs. 

" A curious modification of habit is shown in 

the hermit crab (111. p. 529), which in early life 

backs into an empty snail shell, which aids in 

protecting it from its enemies. The abdomen, 

thus covered, becomes soft and flabby. As 

growth proceeds the necessity arises for a larger 

Sow bug s hell, and the crab goes l house-hunting ' among 

the empty shells along the shore, or it may forcibly extract 

the snail or other hermit from the home which strikes its 

fancy." 1 

Among the relatives of the crayfish that live in damp 
places on land are the pill bug and the sow bug (111. above), 
which are often found beneath water-soaked wood. 

Economic importance of the crustaceans. Crayfish are 
highly esteemed as food in Europe, particularly in France, 
and special efforts are made to increase their number. In 
this country, however, they have, as yet, been used but little 
as food. Their 
principal use is for 
bait in catching 
certain kinds of fish. 
The lobster is to 

bnrimp 

us what the cray- 
fish is to Europeans. While they are not abundant enough to 
be considered a very important source of food, still the fisher- 

1 From Jordan and Heath, Animal Forms. Used by permission of D. Appleton 
& Company, publishers. 







CRUSTACEA AND HUMAN WELFARE 531 

men, in 1930, received $3,900,000 for the lobsters caught. They 
are considered rather as a delicacy, since they are too expen- 
sive for general use, principally on account of their scarcity. 
For a number of years the United States Government made 
efforts to increase the number of lobsters by artificial propa- 
gation. Some states have passed laws forbidding the catch- 
ing of immature lobsters and lobsters with eggs attached. 

Other crustaceans that are used for food are prawns, 
shrimps (111. p. 530), and certain kinds of crabs. Nearly 
all the crustaceans eat dead animal food ; consequently 
they are useful in keeping the water free from dead material. 

QUESTIONS AND APPLICATIONS 

1 . What are the uses of the big claws to the crayfish ? 

2. Which region is segmented? What is the meaning of the word 
cephalothorax ? 

3. How many pairs of legs are used in walking? 

4. How is the crayfish able to swim ? Explain fully. 

5. How are the gill filaments adapted for interchange of gases? 

6. How do the gill filaments differ from those of a fish? 

7. How does a crayfish get oxygen to the gill filaments and carry carbon 
dioxid away? 

8. Describe an experiment the purpose of which is to show that cur- 
rents of water pass through the gill chamber. 

9. How is a crayfish protected by its covering, and by its colors ? 

10. Describe the situation of the eyes. 

11. What can a crayfish do to protect its eyes from injury? 

12. What is the use of the larger pincers? 

13. State the importance of the crayfish as a scavenger and as a source 
of food. 

. 14. How does a crayfish get energy? 

15. How is molting a necessary process? 

16. How are the tiny crayfishes protected? 

17. Name several relatives of the crayfish and state their economic 
importance to man. 

18. What crustacean goes house-hunting and why? 



532 ANIMALS AND HUMAN WELFARE 

PROBLEM 8. HOW ARE OTHER ANIMALS RELATED TO 
HUMAN WELFARE? 

Annelida 

Earthworm. The most common representative of the 
annelida (a-nel'i-dd) is the earthworm. (See 111. below.) 
The general form of this animal is long and cylindrical. If 
one places an earthworm on the ground, it will start to crawl 
away or bore into the soil. Observe that the end that is 
foremost is tapering. This is the anterior end. The oppo- 
site or posterior end is broader and considerably flattened. 



^ -Mouth 
opening 



Earthworm 



The part of the body on which the worm crawls is the ven- 
tral surface, which is somewhat flattened, while the dorsal 
surface is rounded. The whole body is composed of rings or 
segments. Somewhat more than one third of the distance 
from the anterior end of the worm several of the segments 
are usually more or less enlarged and form the girdle. 

At the anterior end toward the ventral surface, there is a 
small opening. This is the mouth, and through it the earth- 
worm sucks in its food, which consists not only of soil, but 
also of leaves of various kinds. Overhanging the mouth is a 
tiny projection, the lip. The animal has no special breath- 
ing organs. The skin, however, is permeated with capil- 
laries, and thus serves as a breathing organ. 



ANNELIDA AND HUMAN WELFARE 533 



Locomotion is brought about by alternately lengthening 
and then shortening one portion of the body after another. 
On the ventral region of the body are rows of bristles, which 
aid in locomotion. The bristles project backward when the 
worm is moving forward, and so keep the animal from slip- 
ping backward when it lengthens itself. The bristles also 
serve to hold the animal in its burrow. 

Earthworms are of very great value in the soil. They 
burrow through the earth by swallowing the dirt which is 
mixed with vegetable matter ; both are then acted upon by 
digestive juices in the alimentary canal. The refuse of the 
food, which is not available for use in the body, is ejected 
from the posterior end of the intestine. The little piles of 
dirt that are sometimes so common 
on a lawn are the " castings " of 
earthworms. It has been found 
that soil worked over by these 
animals is in better condition for 
the growth of plants. Then, too, 
the deeper soil that has not been 
used by plants is brought to the 
surface and mingled with the dirt 
recently used. Darwin l estimated 
that in England earthworms annu- 
ally bring to the top of the ground 
eighteen tons of soil per acre. 

Relatives of the earthworm. Two forms of animals that 
formerly were classed with the earthworm under the head 
of " worms " are the tapeworm and trichina (tri-ki'nd) 
(111. above). The tapeworm is sometimes present in beef, 
and trichina in pork. Meats, therefore, should be well 
cooked to kill all such parasites. The trichina, if it gets 

1 From Darwin's Vegetable Mold and Earthworms. 




Trichina 
Between bundles of muscle. 



534 ANIMALS AND HUMAN WELFARE 

into the human system, causes great suffering. When a 
tapeworm becomes attached to the human intestine by the 
suckers and hooks on its anterior end, it is difficult to 
dislodge, and since it absorbs a considerable amount of 
digested food, it frequently causes emaciation. 



"Mouth 




Posterior^ 
sucker 



Sandworm Medicinal leech 

From, Woodruff's "Animal Biology" 

Two relatives of the earthworm 




The real relatives of the earthworm are represented by the 
sandworm and the leech (111. above). The sandworm is 
often used by fishermen for bait. The medicinal leech was 
formerly much used by doctors to suck blood from certain 
parts of the body ; hence a doctor was often called a " leech." 

Mollusc a 

Fresh-water mussel. The fresh-water mussels are mol- 
lusks that are sometimes called clams. They are often quite 






Incur rent siphon 

Excurrent siphon ! 

Oldest \ 

region of 
shell 




^>:£&5?;f 



MOLLUSCA AND HUMAN WELFARE 535 

abundant on the bottom of creeks, rivers, ponds, or lakes. 
Usually they are partly covered with sand or mud (111. below), 
sometimes even more than is shown here. It will be seen at 
once that the mussel is inclosed by a shell. This consists of 
two parts called valves; hence these animals, as well as salt- 
water mussels, clams, and oysters, are 
called bivalves (Latin bis = two + valve). 
The two valves are held together along 
one margin by a tough material that 
serves as a hinge. On each valve near 
the hinge, a prominence, known as the 
beak or umbo, may be readily seen. 
Around the umbo, in ever widening 
concentric rings, are the lines of growth 
of the animal, which indicate various 
stages in its development. 

Let us now pull up a mussel and lay 
it on a sandy bottom in an aquarium. 
In a few moments the shell will open 
somewhat and from one end will project a pinkish body, which 
may finally extend some distance. This organ is the foot 
If we watch long enough, we may see the mussel use the foot 
to push itself over the surface of the sand, or it may burrow 
into the sand and finally come to occupy a position like that 
in which we found it. 

Now if one is patient, and the animal feels at home, it will 
be possible to see the method of eating and breathing. At 
the end opposite the foot there may slightly project from the 
shell a fringed and somewhat tubular-shaped structure. Let 
us place a little finely powdered carmine in the water above 
the opening. As the carmine slowly sinks and comes oppo- 
site the tube, the particles will suddenly be drawn into the 
tube. This shows that water is being sucked into the tube, 



Foot for burrowing 
in sand 

Clam 

What is the youngest part 

of the shell ? 



536 ANIMALS AND HUMAN WELFARE 

and it brings with it oxygen and any food that may be near, 
such as microscopic plants and animals. 

To learn any more about the feeding and breathing of the 
mussel it will be necessary to open the shell. Let us take 
another mollusk and pry open the valves. We shall soon 
find that this is not easy to do. The valves are held together 
by strong muscles. So we pry the valves open a little with 
a heavy knife and then slip another sharp knife in close to 
the valve, where we meet an obstruction toward one end. 
When we have cut this, the valve opens at that end. After 
cutting the muscle at the other end, we can readily separate 
the valves. All over the surface of the animal, except where 
the two muscles were attached to the shell, is a thin cover- 
ing called the mantle. By raising the body of the mussel from 
the valve it will be evident that there is a similar structure 
on the other side. 

Now, if we fold back the mantle, it will be possible to 
follow the course of the food and water. The first thing that 
strikes our attention is the contracted foot, and above this 
is a soft mass called the abdomen. In the abdomen are 
found the digestive organs. On each side of the abdomen are 
two broad, thin flaps, the gills, by which the animal breathes. 
Between the foot and the end that was buried in the sand 
are found, on either side of the body, two small flaps, or palpi, 
and between them lies the mouth opening. To this mouth 
the food that has been swept into the tube is brought by the 
waving of thousands of cilia that are found on the surface 
cells of the gills and palps. 

Let us now return to the study of the mussel partly cov- 
ered by the sand. The hinge is on the dorsal region of the 
body, the free edges of the valves on the ventral, while the 
mouth and foot are at the anterior end. Hence, the animal 
in its natural position " stands on its head," or at least where 



MOLLUSCA AND HUMAN WELFARE 537 



its head ought to be. From the posterior end projects the 
tubular structure to which reference has been made. 

Let us again drop some powdered carmine closer to the 
animal, and watch the particles when they reach a point just 
above the tube where we saw the particles enter. We shall 
now see the carmine carried away from the animal instead 
of into it. A closer examination reveals the fact that the 
tubular structure has a second opening above the first. 
Both of these tubes are called siphons, the lower being the 
incurrent siphon, and the upper the excurrent siphon. The 
stream of water forced out of the excurrent siphon carries 
with it the carbon dioxid and other wastes of the body. 

Relatives of the mussel. Some of the relatives of the 
mussel are the clams, oysters, salt-water mussels, snails (111. 
at right), and 

Shell - .. ^tf~z»^ Tfck. Opening 



Eyes 




- -^Feelers 



~~Mouth 



Foot 

Snail 
What is the youngest part of the shell ? 



slugs. While 
the fresh-water 
mussels are not 
much used for 
food, they are 
important eco- 
nomically on 
account of the 
pearly matter 
that is found on the inside of their shells. This is used in 
making buttons and other articles. In fact, there is a con- 
siderable industry in this line along the Mississippi River. 

Oysters are important as an article of food. The oyster 
fishermen receive annually more than fifteen millions of 
dollars from these mollusks collected from the oyster beds 
along the Atlantic coast. A certain kind of mollusk, known 
as the pearl oyster, secretes within its shell the valuable 
pearls of commerce. Other mollusks, such as river mussels, 



538 



ANIMALS AND HUMAN WELFARE 



clams, and oysters also form pearls. The inner layers of the 
fresh-water mussel shell is composed of material similar to 
that found in pearls. This material (mother-of-pearl) is 
used in great quantities in the manufacture of pearl buttons 
and pearl-handled knives, 

CCELENTERATA 

Hydra. A study of a fresh-water ccelenterate (se-len'- 
ter-at), known as hydra (111. below), will give one a fair idea 



Tentacle - 

Nettling cells - 



Young sperm cells 
Digestive cavity- 
Mature egg- - 



Embryo*- ■ 
hydras \ 



Mature 

sperm cells 




— Young 
tentacle 



Bud 
Young egg 

— Base of hydra 




Two specimens with buds, 
one contracted 



Diagrammatic longitudinal section 
Hydra 
Left, section through the body. Right, two hydras, one extended and with two buds ; 

the other contracted. 

of the structure and adaptations of this group of animals. 
Hydra is a small animal found in fresh water attached to 
water plants, and sometimes to surfaces of stones or other 
objects on the bottom. At the upper end of the tiny cylin- 
drical column are threadlike bodies known as tentacles. If 



CCELENTERATA AND HUMAN WELFARE 539 

the animal is touched with a needle or pencil, it contracts its 
body and tentacles so much that it can scarcely be seen. But 
in a short time it expands again. 

If the hydra happens to be hungry and some small form 
of animal comes in contact with the waving tentacles, the 
hydra ejects microscopic threads from certain cells (nettling 
cells) in the tentacles. The animal thus attacked is be- 
numbed, and the hydra then uses the tentacles to push its 
prey into a mouth opening in the center of the circular row of 
tentacles. The food is drawn into the inside of the column, 
which is simply a hollow tube (111. p. 538). Here certain 
cells secrete digestive ferments which dissolve the foods 
that the animal has eaten, and the indigestible matter is 
ejected from the mouth. The digested food is then ab- 
sorbed by the cells lining the cavity. Since the animal is 
bathed outside and inside by water containing oxygen, the 
cells are able to absorb oxygen from the water and to give 
off carbon dioxid to the water. Hence no breathing organs 
are needed. 

It is evident that the tentacles with the nettling cells also 
serve to protect the hydra from too great familiarity on the 
part of visitors that might otherwise use it for food. When 
the hydra moves from one place to another, it bends over 
until the ends of the tentacles touch the surface on which it 
rests. The tentacles then adhere to this surface, the bottom 
of the column lets go, and the animal turns a somersault 
and lands on the lower part of the column ; the process may 
then be repeated. 

Like the higher animals the hydra reproduces by means of 
eggs and sperms. But it also has another interesting way of 
producing new individuals. On the surface of the column 
one frequently sees little bunches. These are called buds 
(111. p. 538). They keep on growing outward till at last lit- 







540 ANIMALS AND HUMAN WELFARE 

tie tentacles and a mouth opening are formed at the tip of 
each. It is now evident that we are looking at a very tiny- 
hydra. Finally the new individuals separate from the 
column and begin an independent life. 
This method of reproduction is known 
as budding. 

Relatives of hydra. Among the rela- 
tives of hydra are the corals (111. at left), 
sea-anemones, and jellyfish (111. p. 384). 
One form of coral, the red coral, is of 
Red coral considerable economic importance. In 

Observe the individual &U the coralg the co l umn seC reteS a 
coral animals fully extended. . . . 

Each can contract and dis- mineral substance within which the 
appear within the horny ma- an i ma l can withdraw when danger 

terial it has secreted. . , T ., „ . , , 

threatens. In the case or the red 
coral this material is horny. It is used for decoration, 
and some communities on the Mediterranean are devoted 
largely to the gathering of this coral, and to making it into 
various forms of jewelry. 

Porifera (Sponges) 

Sponges. The sponges are animals less complex in struc- 
ture than the Ccelenterates, although they are composed of 
many cells. Nevertheless, they are comparatively simple in 
structure since they have no digestive, circulatory, respira- 
tory, or nervous system, and therefore each cell has to carry 
•on practically all the necessary nutritive functions. 

Sponges differ largely in the kind of skeletons that they 
possess. In the common bath sponge (111. p. 541) this is 
composed of a tough, horny material. When sponges are 
ready for market, only the horny skeleton remains, the living 
cells having been killed and removed. The sponge skeleton 
;shows a large number of pores in the outer surface, and for 



PORIFERA AND HUMAN WELFARE 541 




A bath sponge 
Each of the many cells of the sponge must 
carry on practically all the nutritive func- 
tions. 



this reason the name Porifera is given to this group of ani- 
mals. The pores lead into canals that run through the body, 
finally connecting with one 
or more larger central cavi- 
ties that lead outward, usu- 
ally at the top. In certain 
parts of these canals there 
are cells with cilia ; their 
action causes water to rush 
into the canals through the 
pores, bringing food and 
oxygen to all the cells of 
which the sponge is com- 
posed. The wastes are 
forced out through the larger canals referred to above. 
Like the bath sponge, all other Porifera are stationary 
in the adult form. 

Protozoa (Single-celled Animals) 

Material for the study of single-celled animals. One way 

of securing an abundance of material for the study of single- 
celled animals is to cut a handful of hay into pieces, put it into 
a quart fruit jar or battery jar, and add plenty of water 
obtained from natural bodies of fresh water, that is, water 
from pond, creek, or swamp. This " hay infusion " should 
be allowed to stand in a warm place for a few weeks. On 
examining the mixture with a low power of the microscope, 
a wonderful scene of life is revealed. Our attention is fixed 
upon a multitude of tiny living forms that hurry across the 
field of our vision. Among these we shall probably find the 
single-celled Paramecium (par'd-me'shi-tmi) which we are 
now to study. The hay is added to the water to furnish food 
for the still smaller living organisms (bacteria) on which 



542 



ANIMALS AND HUMAN WELFARE 



Paramecium feeds. Since these animals will not appear 
unless individuals of the same kind are present, we can see 
the reason for securing the water from swamps or ponds, 
since the public water supplies are frequently treated with 

chemicals that de- 
stroy plant and ani- 
mal life. 

The structure of 
Paramecium. In 
form Paramecium re- 
sembles somewhat 
the shape of a slip- 
per, hence it is some- 
times called the 
" slipper animalcule." 
(See 111. at left.) 
Extending from all 
parts of its outer sur- 
face are many tiny 
projections of proto- 
plasm that look like 
colorless hairs ; these 
are known as cilia. 
In locomotion the 
animal usually moves with the blunt end {i.e. heel of the 
slipper) in front, being propelled by the swifter backward 
strokes of the cilia, with a slower recovery. When Parame- 
cium runs into an obstacle, the action of the cilia is re- 
versed, and thus the animal is enabled to move with the 
opposite end (toe of the slipper) in front. Most animals 
that swim {e.g. fishes and frogs) have broad and flat appen- 
dages that are comparatively large. In Paramecium, on the 
other hand, the organs of locomotion (cilia), while slender, 



Contractile vacuole 
with canals 



Macronucleus 
< large nucleus ) *"* 

Micronucleus 
(small nucleus) W 

Gastric vacuole -f : 



Contractile 
vacuole 



Cilia-' 




,' Groove 
-Mouth 

Gullet 



%— Gastric 
vacuole 



.. Trichocysts 
( nettle cells ) 



Paramecium 
Trace the course of food from the water into a gas- 
tric (food) vacuole. Compare the two nuclei, and the 
two excretory vacuoles. 



PROTOZOA AND HUMAN WELFARE 543 

are so numerous that they accomplish the same purpose as 
the broad swimming appendages of the frogs and fishes. 

How Paramecium secures and digests its food. A Para- 
mecium feeds upon one-celled plants and animals. On one 
side of the animal is a furrow, or groove, which is lined with 
cilia (111. p. 542). At the lower end of the groove is an open- 
ing, the mouth, which leads into a short tubular gullet. The 
rapid inward motion of the cilia within the groove draws the 
food toward the mouth, and other cilia lining the gullet push 
inward the food particles. Small collections of these food 
particles are made at the lower end of the gullet, and these 
masses, food balls, are circulated within the cell by the 
streaming movement of the protoplasm. 

As the food balls circulate through the protoplasm, they 
are gradually digested by ferments made by the protoplasm, 
and the food materials thus liquefied are used, as in plants and 
other animals, for the production of more protoplasm, or for 
the release of energy needed for locomotion and for food 
getting. The indigestible parts of food are forced out 
through an opening that appears in the side of the body. 

How Paramecium carries on respiration and excretion. 
Since a Paramecium is surrounded by water that contains 
oxygen, this can pass into the protoplasm by diffusion through 
the thin membrane surrounding the animal. When the 
oxygen combines with chemical elements found in foods or 
protoplasm, oxidation is carried on, energy is released, and 
waste substances are formed. The carbon dioxid diffuses 
outward into the surrounding water through the outer layer 
of the animal. 

Toward either end of the animal is a clear space which is 
circular and accompanied by smaller spaces, which together 
have at times a star-shaped appearance. These are the 
contractile vacuoles. The liquid wastes, mainly water, col- 



544 



ANIMALS AND HUMAN WELFARE 



lect in these vacuoles. The protoplasm then periodically 
presses upon the vacuoles, and the waste materials are 
squeezed out of the animal into the surrounding water. 
When this occurs, the contractile vacuoles disappear for an 
instant. They then slowly refill. These vacuoles also 

probably help to 
keep the Para- 
mecium from 
bursting from 
the internal pres- 
sure resulting 
from osmosis of 
water. 

Reproduction 
of Paramecium. 
In the interior 
of a Paramecium 
are two nuclei, 



Mic'ronucleus — --! 



Gullet 



Micronucleus — ^ 

Gullet - 




Contractile 
vacuole 

Macronucleus 
\ large nucleus ) 

H. Contractile 
vacuole 



Contractile 
vacuole 



Macronucleus 

( large nucleus ) i ,-, 

v y ' known as the 

large nucleus and 

the small nucleus. 

Both of these 

show readily 

when the animal 

is stained with 

iodine or with 

other chemicals. When the animal reproduces, the nuclei 

divide in halves (at least in one species of Paramecium), a 

new mouth and gullet are formed, and two new contractile 

vacuoles appear (111. above). The cytoplasm then divides 

transversely, the two cells separate from each other, and thus 

from a single individual two new individuals are formed. If 

conditions are favorable, both animals grow and may in turn 



♦ Contractile 
vacuole 



Paramecium dividing 

Compare with the illustration on page 542, and state changes 

in nuclei and in vacuoles. 



PROTOZOA AND HUMAN WELFARE 545* 

reproduce at the end of twenty-four hours. It has been esti- 
mated that a single individual may be responsible for the 
production of 268,000,000 offspring in one month. Actually, 
however, this never takes place, for the necessary food, 
oxygen, and other favorable conditions would soon cease to 
exist. In the " struggle for existence " many individuals 
would die, and only those that are strongest would survive. 

EXERCISE 71 
Study of Paramecium. Laboratory study. 

On a glass slide, by means of pipette or glass tube, put a drop of the 
hay infusion containing Paramecium. Study the preparation with the 
low power of the compound microscope. 

1. What is the color of the living animals? 

2. Do they seem to swim slowly or rapidly? Do they really swim as 
rapidly as they appear to ? Give a reason for your answer. 

3. Is the more pointed end or the rounded end of the animal usually 
foremost in swimming? 

4. What does a Paramecium do when it strikes an obstacle ? 

5. Does the animal ever rotate on its long axis? If so, can you tell 
how it does this ? 

m r ^^K Food vacuole 

The structure of \5§Kj xr , 

, „..._, N^v'v^S*^ Nucleus 

an amoeba. When x ^°6p^r^ / 

we study with the /^ : ;?^W?£3S^ ^——-^ 

compound micro- <-^_J> MSf #w. ^-^^y^ 

scope some of the ^- — c^'?^' ' '■■ ^xT" 

mud, decaying ^7^/^^ 

i ,i_ v Contractile' r^ ^s 

leaves, or other sedi- vacuole ^^ 

ment obtained from Amoeba 

the bottom of a pool Which parts are living and which are Uf eless ? 

of water, or even in a hay infusion, we may be fortunate 

enough to run across specimens of another very interesting 

form of single-celled animal, known as theamceba (111. above). 



546 ANIMALS AND HUMAN WELFARE 

This minute creature is a droplet of semifluid, more or less 
colorless protoplasm. It may be somewhat spherical in form ; 
but as we look at our specimen, we note that its shape is 
changing (111. p. 545). On one side, some of the material of 
which the amceba is composed is slowly streaming out to 
form one or more projecting processes, which vary in size 
and shape. Each of these extensions is called a " false foot," 
pseudopod (su 'do-pod). These may increase in size until 
all of the substance of the animal has passed into them. By 
pushing out these processes in front and pulling up its body 




An amoeba securing a food particle 
What structures within the animal can you see ? 

matter from behind, the amceba moves slowly from one 
part of the slide to another. If we suddenly jar the slide, all 
the protoplasm in the extended false foot is drawn back 
toward the center of the animal, and the amceba again 
assumes its spherical form. 1 

Likenesses and differences between Paramecium and 
amceba. Both Paramecia and amoebae are animals so 
small that they can barely be seen with the naked eye. 
Both live in water, both are one-celled animals, and both 
carry on the same functions, but in a somewhat different 
manner. While a Paramecium maintains a relatively fixed 
form, the amceba is capable of assuming almost any shape. 
A Paramecium has two nuclei and two contractile vacuoles ; 
an amceba, on the other hand, has only one of each. 

1 For reproduction of amoeba see p. 211. 



PROTOZOA AND HUMAN WELFARE 547 



Unlike Paramecium, the amoeba has no definite part of 
the body through which it takes in food. When this animal 
is feeding, it slowly flows about the one-celled plant or animal 
and finally engulfs it (111. p. 546). The processes of digestion, 
assimilation, respiration, excretion, and reproduction are 
much the same in both. These organisms belong to a group 
of animals known as the Protozoa. 

Importance of Protozoa to man. Most of the Protozoa 
serve as food for other animals that live in the water, and 
these in turn are fed upon 
by fish, which may be eaten 
by man. Thus the one-celled 
plants and animals are found 
to be an important food basis 
for human beings. 

Some of the Protozoa that 
live in the sea secrete tiny 
shells (111. at right), and when 
the animals die, the shells drop 
to the bottom. As a result 
of heat, pressure, and other 
causes, this bottom " ooze " is 
gradually solidified to form chalky rocks. In the upheavals 
of the ocean bottom that have taken place in the ages past, 
these rocks have often been forced above sea level. The 
chalk cliffs of Dover, England, were formed in this way. 

While most of the Protozoa are harmless, there are a few 
forms that have become parasitic in human beings. Malaria 
is due to a protozoan resembling an amoeba in form. This 
parasite, as we have already learned, is carried from one 
victim to another by the female Anopheles mosquito. When 
this organism of malaria is present in human blood, it bores 
its way into a red corpuscle (111. p. 548), feeds upon the con- 




Skeletons of Protozoa 

Shells like these form the white chalk 
cliffs of Dover, England. 







Stages in human body 




f*) 



Male cells 




Stages in mosquito's stomach 



, Swellings on stomach wall 



Fertilized 
cell 




Mosquito's 
stomach 



Section of swelling 

containing 
malarial protozoans 



Section of salivary glands 
containing 
malarial protozoans 



Life history of the malaria protozoan 
Above, asexual reproduction in human blood. Center, sexual reproduction in mos- 
quito's stomach. Below, malarial parasite in the organs of a mosquito. 



PROTOZOA AND HUMAN WELFARE 549 



tents of this blood cell, and grows at the expense of the cor- 
puscle until the parasite occupies nearly all the space inside 
it. The malaria parasite then divides into a number (6-16) 
of daughter parasites, which 
rupture the red corpuscle in 
which they have been de- 
veloping and escape into 
the liquid part of the blood, 
thus causing the chills so 
characteristic of malaria. 
Each new parasite then at- 
tacks a new corpuscle and 
at the end of two or three 
days produces six to sixteen 
new spores, and so the or- 
ganisms multiply. For the 
treatment of malaria qui- 
nine is the most effective 
drug known at present. It should be taken in the quantity 
and at the times prescribed by the physician. 

Another form of Protozoa causes the terrible disease known 
as sleeping sickness of tropical Africa (111. above). This 
single-celled animal is transmitted from one victim to 
another by a kind of fly known as the tsetse fly (tset'se). 
Tropical dysentery is also caused by a protozoan. 




Courtesy of American Museum of Natural History 

Protozoans that cause sleeping sickness 
The circular bodies are blood corpuscles. 



QUESTIONS AND APPLICATIONS 

1. In what ways does an earthworm differ in structure from an 
insect? 

2. Describe the earthworm's method of locomotion, eating, and breath- 
ing. In what ways are these animals beneficial to man? 

3. Name four relatives of the earthworm and show how each is bene- 
ficial to man. Look up Darwin's studies of the earthworm. 

4. Describe the shell and the internal organs of a bivalve mollusk. 



550 ANIMALS AND HUMAN WELFARE 

5. How are locomotion, feeding, breathing, and excretion performed by 
a clam? 

6. Name some of the relatives of the mussel and give the economic 
importance of each. 

7. How does a hydra carry on locomotion and secure and digest 
its food? Describe its two methods of reproduction. 

8. What are some of the relatives of hydra and how are they important 
economically ? 

9. How do sponges differ in structure from all the other animals we 
have studied ? How does a sponge carry on each of its functions ? 

10. Look up the method of collecting and preparing commercial sponges. 

11. How would you go to work to secure material for the study of 
(a) Amoeba, (6) Paramecium? Give your reason for each step. 

12. State in detail the resemblances and the differences between Para- 
mecium and Amoeba as to (a) shape, (b) nucleus, (c) contractile vacu- 
oles, (d) method of locomotion, (e) breathing, (/) excretion of wastes, 
(g) method of reproduction. 

13. In what two ways are the Protozoa useful to man? 

14. What three diseases are due to Protozoa ? Study the illustrations 
on pages 548 and 549 and describe two of these disease-producing proto- 
zoans. 

15. How does Paramecium prevent excessive internal water pressure 
from acting on it as it did on the egg (see 111. p. 81). 

16. In what one respect are the Annelida like the Arthropoda, and in 
what one respect are they different? See page 551 and illustrations on 
pages 532 and 534. 

17. Find out how and where pearls are formed. What is "mother-of- 
pearl"? 

18. In what forms of food may the parasitic " worms " trichina and tape- 
worm be present? 

19. How may the foods named in your answer to 18 be made safe for 
consumption ? 

20. Of what advantage is the United States Government inspection of 
meats ? 

21. How is an earthworm able to resist being pulled from its burrow? 

22. How do Ccelenterata differ in structure from Arthropoda, Annelida, 
and Mollusca? See pages 551 and 552. 

23. What part of the animal is present in the bath sponge when ready 
for use? 






O 

Q EH 

M 

^ R 
23 


By means of legs 
and wings in in- 
sects 

By means of legs, 
abdomen, and 
swimmerets in 
crayfish 


Earthworms 
carry on loco- 
motion by 
elongating 
and contracting 
the segments, 
aided by bristles 


Oysters are fixed 
in adult stage 

Clams and snails 
carry on loco- 
motion by means 
of a muscular 
"foot" 


Eh 

n w 


By means of 
jointed mouth 
parts 


By means of 
sucking mouth 
at anterior 
end 


By means of 
cilia in clams 
that bring 
food into 
mouth; by 
rasping tongue 
in snails 


§1 

e 3 

Eh a 


By means of 
air tubes in 
insects ; gills, 
in Crustacea 


to 
co co 

a? a 

o 
pq 


By means of 
gills, or soft, 
moist skin 


CO 

o 

►J CO 

si 

o « 

<! 
w 
o 


Segmented body, 
jointed 
appendages 


Parts of the 
elongated 
body arranged 
in rings. No 
jointed ap- 
pendages 


Soft body, usu- 
ally covered 
by shell 


£0 

H 

►J 

Cm 

§ 

X 


Insects 

Crustacea 

Spiders 


Earthworm 

Leech 

Sandworm 


Oyster 

Clam 

Snail 


^ M 

° s 
2« 


■+3 

CD 
CD 

o3 t ~ 

O CD 

o a 

< 


O bQ 

-° .a 

*-< 
03 ° 
TS cd 

CD o3 

< 


i 

CO 

03 *& 
O CD 

CO .S 

a o 

O JO 



fc fe 

O O 

Q £ 

° 2 

&H O 

S3 


Corals are fixed in 
mature stage 

Jellyfish carry on 
locomotion by 
enlarging and 
contracting the 
bell-shaped body 


Have locomotion 
only while very 
young 


By means of cilia 
or by the move- 
ment of all the 
protoplasm 


p 2 

2 Q 


By means of 
tentacles sup- 
plied with 
stinging cells 
which bring 
food to mouth 


By means of 
cilia, currents 
of water bring 
food to all 
the cells 


By means of 
cilia or pseu- 
dopods 


Eh a 

s £ 


Cells of exterior 
and interior 
bathed by 
water from 
which oxygen 
is secured 


By means of 
cilia, currents 
of water bring 
oxygen to all 
the cells and 
remove the 
wastes 


CD 13 

J g 

2 S3 


CO 

o 

|J CO 

K « 

fe 5 

o 2 

<! 

a 
O 


Body cavity and 
digestive cav- 
ity one and 
the same 


Pores all over 
the body; 
many-celled, 
but without 
digestive, cir- 
culatory, or 
nervous sys- 
tem 


This group in- 
cludes all the 
single-celled 
animals 


CO 

W 


CO 

CD 

Si 

g >> 


o "" 


a 

CD 03 

§ 8 


O H 

O 

H fe 

S5« 


Ccelenterata (hol- 
low digestive 
tract) 


k 

o 

3 

g.a 
«s * 

ra CD 

c3^ 

Ph 


1 

co 

ll 

O 03 

Ph 






UNIT X. MAN IN RELATION TO HIS 
ENVIRONMENT 

PROBLEM 1. HOW ARE PROTECTION AND LOCOMOTION 

SECURED ? 

How the Skin Is Useful to Man 

Characteristics of the skin of man. The whole outer 
surface of our bodies is incased in a flexible, elastic skin of 
varying thickness and texture. In regions like the palm 
of the hand and the sole of the foot, for instance, the skin is 
thick and tough, while the covering of the lips is extremely 
thin. At the ends of the fingers and toes are the nails, and 
all parts of the body, with the exception of the palms of the 
hands and the soles of the feet, are covered with hair, which 
varies both in length and density. Both the hair and the 
nails are modified parts of the skin. 

Functions of the skin. The most obvious use of the skin is 
the protection it affords for the muscles and other organs 
that lie beneath. In the second place, it has a countless 
number of sense organs which receive messages from the 
outside of the body. These messages are hurried in along 
nerve fibers to the spinal cord and brain ; and in this way 
we then get impressions of temperature, of pressure, and of 
pain. Again, by means of the perspiratory (per-spir'd-to-n) 
action of the skin, the body throws off a great deal of water 
and small quantities of other waste matters which form the 
sweat. And, finally, as a result of the evaporation of this 

553 



554 



MAN AND HIS ENVIRONMENT 



Pores of sweat glands 



water from its outer surface, the body loses its surplus of 
heat and so keeps an even temperature. 

Characteristics of the layers of the skin. The skin every- 
where consists of two distinct layers : an outer, called the 

epidermis (from the 
Greek, meaning out- 
side skin), and an 
inner, the dermis 
(111. at left). When 
one gets a blister 
by burning the skin, 
most of the epi- 
dermis is lifted up 
by an excessive 
amount of lymph 
that comes out of 
the blood capillaries 
and lymph vessels. 
In a blister one can 
easily distinguish 
the white epider- 
mis from the pink 
layers of the dermis 
lying beneath. 

When one washes 
with soap and water 
the surface of a por- 
tion of one's body 
and then rubs it 
vigorously, one will find that thin layers of the outer skin are 
easily removed and rolled into tiny cylinders. If a needle 
be inserted into the skin that covers a blister, the touch of 
the needle will be felt, but no pain is caused, nor does the 




Epidermis 
Papilla 

Dermis 

J- —Nerve 
Sebaceous 



Subcu- 
taneous 
tissue 
'Ducts 
from 
—sweat 
glands 



^Artery to 
l-—Bulb gland 

&-- Papilla containing capillaries 
W and nerves 

—Nutrient artery to hair 

Section of skin and underlying tissues 
In which layer are the sweat and sebaceous glands found ? 






SECURING PROTECTION AND LOCOMOTION 555 

blood flow. By means of these simple experiments we learn 
the following facts in regard to the epidermis : (1) the outer- 
most layers are being constantly worn away, and hence we 
infer there must be a constant growth from beneath to 
replace this loss ; (2) blood vessels are lacking in the outer 
skin ; and (3) nerve fibers of touch, but not of pain, are 
present in the epidermis, for we are conscious when the 
covering of a blister is touched, but we feel no pain. 

In the dermis and in the fat layers beneath the skin (sub- 
cutaneous tissue) are found the blood vessels, most of the 
nerves, and the sweat and the oil glands (111. p. 554). 

Importance of bathing. The oil (sebaceous, se-ba'sh#s) 
and perspiratory glands (111. p. 554) are constantly pouring 
their secretions in greater or less quantity upon the skin. As 
the water evaporates, the oil and the solid ingredients of the 
sweat are left behind. Unless these are removed, they tend 
to clog the openings of the ducts from the glands and so inter- 
fere with the work of the skin. A considerable amount of 
these substances is doubtless worn away, together with the 
scales of the outer skin, by friction against the clothing. 
But if the skin is to carry on its functions to the best advan- 
tage, frequent baths must be taken. 

Kinds of baths. The oily secretions and much of the 
accumulated dirt on exposed surfaces of the skin can be 
removed only by the use of warm water and soap ; hence 
these should be employed upon the hands two or three 
times a day, especially before eating, and at least once or 
twice a week upon the whole body. Warm baths should 
be employed, however, for their cleansing effect only, since 
they are usually followed by a feeling of lassitude. One is 
much more likely to catch cold, too, after exposure to warm 
water, as it opens the pores of the skin, causes the arteries 
near the surface to dilate, and thus increases the amount of 



556 MAN AND HIS ENVIRONMENT 

perspiration. Unless the warm bath is taken just before 
one goes to bed, it should be followed by a quick application 
of cold water. 

Cold baths, on the other hand, if taken under proper con- 
ditions, have an exhilarating effect. The best time for such 
a bath is immediately after one rises in the morning. Until 
one becomes accustomed to the cold temperature, the water 
may be applied with a sponge. The body should then be 
rubbed vigorously with a towel. In our study of the cir- 
culation we referred to the effect of heat and cold upon the 
arteries. After their first contraction caused by the contact 
of the cold water with the skin, the blood vessels enlarge, 
and one feels all over the body a warm, healthful glow. 
Cold baths should never be taken immediately after one eats, 
since the blood is thereby drawn away from the organs of 
digestion. Nor should one remain in cold water until one 
feels a chill. If the warm reaction does not take place after 
the bath, the latter is not beneficial, but injurious. Cold 
baths are undoubtedly one of the best means of protecting 
the body against colds. Shower baths, however, are better 
than a cold plunge, for they stimulate both by the cool 
temperature of the water and by the force with which it 
strikes the skin. 

Care of the hair. The oil glands are most numerous in the 
scalp ; and if the skin is in a healthy condition, the hair is 
supplied with just the proper amount of oil. If this secre- 
tion dries, however, and becomes mixed with the loose outer 
scales of the epidermis, dandruff is caused, and this should 
be removed by vigorous brushing and shampooing. Not 
only is the scalp cleaned in both of these ways (if clean 
brushes and combs are used), but the friction stimulates the 
circulation of the blood through the scalp, and good blood is a 
better hair tonic than any external application. If the oil 



SECURING PROTECTION AND LOCOMOTION 557 

supply is insufficient and the hair becomes dry, liquid vaseline 
may be used. The scalp should be well dried after a bath, 
for moisture at the roots of the hair tends to cause decom- 
position on the scalp. 

Care of the nails. One of the surest means of detecting 
slovenly personal habits is by observing the care an individual 
takes of his finger nails. An accumulation of dirt beneath 
the nails or jagged edges caused by biting the nails almost 
always indicate a want of good breeding. The finger nails 
should be carefully cleaned with soap, water, and a nail 
brush or with a nail cleaner, but never with a penknife or 
scissors, for metal roughens the surface and thus makes 
places for the lodgment of dirt. The most convenient 
method of trimming the nails is in a curved direction, and 
this gives them the best appearance. It is better to shape 
the nails with a file than to cut them. The roll of epidermis 
about the base of the nail should frequently be pushed back 
after the hands have been soaked in soap and water ; other- 
wise this outer skin is likely to become torn and to form the 
so-called " hangnails." These are often a source of great 
discomfort and sometimes of danger, for they furnish a pos- 
sible opening for infection by bacteria. 

Treatment of burns. We have already suggested the 
treatment for cuts and bruises of the skin in connection with 
the blood system and bacteria (p. 353). Another form of 
accident that may injure the skin is a burn. The affected 
part should be covered with a paste of baking soda, which 
tends to lessen the pain by keeping out the air and by 
reducing the inflammation. A mixture of equal parts of 
linseed oil and limewater (known as carron oil) is also a good 
remedy to keep on hand for burns. If the clothing of a 
person catches fire, the flames should be extinguished by 
wrapping him quickly in thick clothing or rugs. 



558 MAN AND HIS ENVIRONMENT 

Regulation of the heat of the body. The temperature in 
the mouth of an adult is about 98.6° F. This does not vary 
to any appreciable extent in winter or summer, no matter 
how vigorously one may exercise. Yet during exertion 
oxidation goes on much more rapidly, and a great deal of 
heat is thereby released. What, then, becomes of this extra 
heat? 

In fevers the temperature sometimes runs up to 105° or 
more. At this time we know that the skin is dry and 
parched, for the body is unable to perspire. We may infer, 
then, that in health we keep cool by perspiring, and such 
proves to be the case. During exercise the heart beats with 
greater rapidity, and the heated blood is driven more rapidly 
through the skin as well as through other organs of the body. 
When it comes in contact with the two and a half million 
sweat glands of the skin, a great deal of water is given out, 
and this soon reaches the surface and collects in drops. In 
evaporating this water the body loses its surplus of heat, 
since the heat absorbed by this water while evaporating 
is taken from the body. When sufficient heat has been lost, 
perspiration practically ceases. By this automatic process 
our bodies keep at an even temperature, whatever may be 
the degree of oxidation within us and in spite of considerably 
cooler or warmer air about us. Dogs cannot cool off by 
sweating, since they have no sweat glands in the skin ; 
instead they pant and extend their tongues to cool them- 
selves. 

Effect of alcohol on body temperature. It is commonly 
but erroneously believed that alcohol warms the body, espe- 
cially after exposure to severe cold or to soaking rains. The 
alcohol causes the muscles in the arteries on the body surface 
to relax and consequently a larger amount of blood comes 
into the skin. This, it is true, gives a temporary feeling of 



SECURING PROTECTION AND LOCOMOTION 559 

warmth. In reality, however, the heat in the blood thus 
escapes all the more rapidly ; hence, there is a loss instead 
of a gain in body temperature. The following account gives 
a vivid picture of the result of taking liquor during exposure. 
" A party of engineers were surveying in the Sierra Nevadas. 
They camped at a great height above the sea level where the 
air was very cold, and they were chilled and uncomfortable. 
Some of them drank a little whisky, and felt less uncom- 
fortable ; some of them drank a lot of whisky and went to 
bed feeling very jolly and comfortable indeed. But in the 
morning the men who had not taken any whisky got up in a 
good condition ; those who had taken a little whisky got up 
feeling very miserable ; the men who had taken a lot of 
whisky did not get up at all : they were simply frozen to 
death. They had warmed the surface of their bodies at the 
expense of their internal organs." * 

How the Skeleton Is Useful to Man 

Why skeletons are necessary. We have already seen 
that the outer coverings of animals — exoskeletons — serve 
as a means of protection. This is likewise true of the endo- 
skeleton of man and of the higher animals. The brain, for 
example, is inclosed in the bony cranium (111. p. 580) ; the 
eyes are set in deep sockets ; the delicate mechanism of the 
inner ear is hidden within the hardest bone of the skull 
(111. p. 587) ; and the organs of the chest cavity are protected 
by the ribs and breastbone. Another use of endoskeletons 
is that they furnish points of attachment for muscles. 
In these cases parts of the skeleton act as levers, which are 
moved by the muscles whenever the animal moves any part 
of its body. In a word, then, skeletons help to give animals 

1 From Sir Thomas Lauder Brunton, Lectures on the Action of Medicine. Used 
by permission of The Macmillan Company, publishers. 



560 MAN AND HIS ENVIRONMENT 

their permanent shape ; they protect delicate organs ; and 
they provide a leverage on which muscles may act. 

For convenience the two hundred bones of the human 
skeleton may be divided into three groups ; namely, (1) the 
bones of the head (skull), (2) the bones of the neck and trunk, 
and (3) the bones of the arms and legs. 

Fractures. Any sudden strain or blow upon a bone is 
liable to cause a break or fracture, especially in later life, 
when the bones are brittle. Fractures occur more com- 
monly in the shafts of long bones, and they may usually be 
recognized by the fact that an extra region of movement is 
thus formed and by the fact that the broken ends grate 
against each other. 

In treating a fracture, the pieces of bone must be brought 
back into position (this is called " setting " the bone) and 
must be held in place by splints until the ends have become 
firmly " knit " together. The setting of a bone should be 
done only by a surgeon. In general but two rules should 
be followed in case of a fracture : First, send for a doctor; 
second, keep the broken bone perfectly quiet in as comfortable 
a position as possible. Hot- or cold-water applications if 
applied at once often reduce the pain and prevent inflam- 
mation. Movement at the point of fracture almost always 
causes inflammation, which makes the setting difficult ; and 
if moved suddenly, the surrounding tissues may be injured 
as well. 

Dislocations. A dislocation is an injury to a joint in 
which the ends of the bones are forced apart. One can 
usually recognize a dislocation by the unwonted protrusion of 
the bones and by the pain caused when any motion at the 
joint is attempted. Since ligaments of connective tissue 
bind the bones together rather closely, a dislocation often 
results in a wrenching or tearing of the connective tissue 



Cranium- 



Collar bone (clavicle\ 



Shoulder blade ** 
(scapula) 

Humerus 



Pelvic bone - — 

Cavity of- 

pelvis 

Carpals*--- 
Metacarpals — 

Phalanges -- 



Femur 



Knee cap- 
(patella) 



Tibia 



Fibula 



Tarsals - 




^Nasal bones 

--Malar (cheek) bone 
- Superior maxillary bones 
-Inferior maxillary bone 
Spinal column 



Breast bone 
(sternum) 

-*Ribs 

Spinal column 

— Radius 
Ulna 



-Tibia 
Fibula 



/Metatarsals 
^-Phalanges 



Skeleton of man 



562 MAN AND HIS ENVIRONMENT 

about a joint; swelling and discoloration follow quickly; 
and it is therefore necessary to put the bones back into place, 
or, in other words, to " reduce the dislocation " as soon as 
possible. If surgical aid can be procured, it is better to 
apply cold water to the joint to keep it from swelling, and 
wait for the doctor's arrival, since by unskillful treatment 
further injury to the joint may result. When skilled treat- 
ment is impossible, most dislocations may be reduced by. 
steadily pulling the bones apart until it is possible for the 
ends to glide back into place. 

Sprains. When a sudden strain causes neither a fracture 
nor a dislocation, it often gives rise to a twisting or tearing of 
ligaments and other connective tissues in the region of a joint. 
Such an accident is called a sprain. The injured region is 
usually swollen and painful. Since it is difficult to distin- 
guish a sprain from other accidents to the skeleton, medical 
assistance should be summoned and the following directions 
carefully followed : (1) the sprained member should be 
placed at once in cold water or in hot water and held there for 
some time ; (2) arnica or witch-hazel may be applied ; (3) the 
sprain should then be bound in a tight bandage (these three 
treatments tend to keep down the swelling) ; and (4) the 
joint should have complete rest until all swelling and soreness 
have disappeared. It is . probable that more permanent 
injuries result from careless treatment of sprains than from 
all other accidents to the skeleton. 

How Motion and Locomotion Are Carried On 

by Man 

Motion and locomotion. Motion seems to be a funda- 
mental characteristic of all living things. It is a property 
of the protoplasm of the simplest plants and animals. In 



SECURING PROTECTION AND LOCOMOTION 563 



the one-celled amceba (p. 545) the whole mass of proto- 
plasm has the power not only of motion within itself but also 
of moving from place to place, which is called locomotion. 

We have seen that even in one-celled animals like Para- 
mecium division of labor within the animal cell is evident, 
since these animals have developed special parts of the 
protoplasm, the cilia, to carry 
on the process of locomotion. 
In higher animals this differen- 
tiation is carried still farther, 
and certain cells have become 
specially adapted to carry on 
all the movements essential to 
life. These specially endowed 
cells are known as muscle cells, 
and the organs of which they 
form the greater part are 
called muscles. 

Muscle cells (111. p. 26) 
have the peculiar power of 
decreasing their length, that 
is, contracting, and hence in- 
creasing their breadth and 
thickness, and then of decreas- 
ing their breadth and thick- 
ness and thereby increasing their length {relaxing). When 
the individual cells contract, the muscle as a whole of course 
shortens, and if the muscle is attached to the bones of an 
appendage, the appendage is moved by it. 

Importance of muscle tissue. Muscle tissue constitutes 
41 per cent, or almost half, of the weight of the human body. 
In this kind of tissue is found one fourth of all the blood. 
But the importance of muscle tissue is appreciated even 




7>*ap< 



Muscles of the head and neck 
Find the muscle that : closes the jaw ; 
pulls the head forward; pulls the head 
backward; pouts the lips; broadens the 
mouth in a smile ; draws down the cor- 
ner of the mouth. 



564 



MAN AND HIS ENVIRONMENT 



Attachment of 

biceps tendon 

to radius 



Attachments of 

biceps tendons 

to shoulder 



more fully when we realize that nearly every kind of move- 
ment in the body is due to the action of the muscles. They 
bring about not only the more obvious motions of the arms, 
the legs, the trunk, and the head, but also all the contractions 
of the heart, of the stomach, and of other internal organs. 
Every change in the expression of the face (111. p. 563) and 
every variation in the tone of the voice is likewise a result of the 
action of this all-important tissue. So we are not surprised 

that there are more 
than five hundred sepa- 
rate muscles, which vary 
in length from the frac- 
tion of an inch (within 
the ear cavity) to over 
a foot and a half (down 
the front of the thigh). 
Kinds of muscles. 
All these muscles are 
in one way or another 
under the control of the 
nervous system. Some of them are directed by the con- 
scious portions of our brain. Thus we can close our ringers 
and open them as we please ; we can move the eyes, the 
head, and the legs at will. We call all the muscles that are 
controlled by our will power voluntary muscles. On the other 
hand, most of the muscles of the throat, those of the gullet, 
stomach, and intestines, act without any voluntary direction 
on our part, and they are therefore called involuntary. 

The biceps muscle. When one places his left hand on the 
front surface of his right upper arm and then draws up his 
right forearm as far as possible, he feels the muscle in front 
of the humerus (111. above) become shorter, thicker, and 
harder. If he extends the forearm again, a tough cord, or 




Biceps 1 Pulls up 
muscle / forearm 
Triceps \ Straightens 
Elbow muscle J forearm 

The muscles that move the forearm 



SECURING PROTECTION AND LOCOMOTION 565 

tendon, can be felt at the lower end of the muscle. This 
tendon attaches the muscle to the radius bone. The upper 
end of this muscle is covered by thick layers of flesh, but if 
these were removed, we should find two other tendons, which 
connect the muscle with projections on the shoulder blade 
(111. p. 564). The muscle we have been studying is called the 
biceps, from the fact that its upper end has two tendons. 
The central portion, or the part that contracts, is called the 
belly of the muscle. 

The triceps muscle. If we straighten or extend the fore- 
arm as far as possible, the belly of a muscle behind the 
humerus is found to swell. This is the triceps muscle, so 
called because it has three tendons at its upper end. These 
tendons form the upper end of the triceps and are attached 
to the shoulder blade and to the humerus. The lower end 
of the muscle is attached to the projecting head of the 
ulna (111. p. 564), namely the elbow. 

Necessary conditions for healthy muscles. If one is to 
have a well-developed and healthy muscular system, four 
conditions must be fulfilled : The body must be supplied 
with nutritious food ; there must be a generous amount of 
fresh air ; the muscles must be exercised vigorously ; and 
this exercise must be followed by periods of rest. We 
shall now consider how some of these requirements may 
be met. 

Exercise. It seems like a contradiction to say that the 
only way to get more and better muscle is to destroy what 
we already have. Every one knows, however, that if the 
muscles of the arm or the leg are not used for a time, they 
become weak and flabby, and yet every time a muscle is 
made to contract, some of its substance is oxidized. New 
muscle must then be formed by the process of assimilation 
to take its place. 



566 



MAN AND HIS ENVIRONMENT 



A certain amount of vigorous exercise each day is essential 
if one is to keep one's body in the best physical condition. 
This amount, of course, varies with the individual. It should 
never be carried to an excess, resulting in exhaustion, but 
should usually be at least the equivalent of a five-mile walk 

or a fifteen-mile bicycle ride. 
Fortunate is the boy who 
can spend the early years 
of his life in the country, 
and who has been taught 
to do a certain amount of 
manual work each day out 
of doors. Regularity in 
exercise is as important as 
regularity in eating. One 
cannot exercise vigorously 
one day and expect its good 
effects to last for a week. 
We should not call upon 
the muscles for violent exer- 
tion immediately after rising 
and before breakfast, nor 
should we exercise until at 
least half an hour after 
eating. The physiological 
reasons for these directions 
have been already given in our study of the circulatory 
system (p. 134). 

The best forms of exercise are those that call into play the 
greatest number of muscles. For this reason gymnasium 
training is better than many kinds of outdoor sports. In the 
gymnasium, too, special forms of exercise can be taken to 
develop any muscles found to be weak. On the other hand, 




Courtesy of American 
Child Health Association, New York 



An example of a well-built body 

Age 15 years, height 67 inches, weight 146 

pounds. 



SECURING PROTECTION AND LOCOMOTION 567 



lawn tennis, golf, rowing, and football have the additional 
advantage of being played in the open air, and games of this 
sort are usually more exhilarating than are set forms of 
exercise with apparatus. To secure the full effect of any 
kind of exercise, it should 
be followed by a moder- 
ately warm, then by a cold 
shower, or sponge bath, and 
by a good rubbing of the 
body with a coarse towel. 

Muscles are not the only 
tissues developed by exer- 
cise. Every muscular con- 
traction is directed by some 
kind of stimulus from the 
nervous system. Before the 
muscles of the arm or leg 
contract, a "message" must 
come to them from the brain 
or spinal cord ; hence nerve 
tissue is likewise developed 
by exercise. When properly 
carried on vigorous exercise 
helps greatly in eliminating 
the wastes of the body 
through the skin and the 
other organs of excretion. 
The exhilaration and the 

sense of self-conquest that comes from successful control of 
the body are among the best rewards of vigorous exercise. 

Rest. If physical exertion is carried beyond a certain 
point, exhaustion results, and the muscles cannot be made 
to contract until after a period of rest. Since all muscular 




Courtesy of American 
Child Health Association, New York 

An example of splendid physique 
Age 13 years, height 63 inches, weight 
1 1 2| pounds. Fine proportion of trunk 
and limbs. 



568 MAN AND HIS ENVIRONMENT 

contraction involves oxidation of tissue, periods of rest must 
be allowed for the muscles to get rid of their wastes and to 
build up new tissue in place of the old. The feeling of weari- 
ness after long-continued exercise is probably due to the 
presence in the body of great quantities of carbon dioxid, 
water, and urea. One can often rest to good advantage by 
changing from one form of activity to another, but from 
eight to nine hours of sound sleep each night are indispen- 
sable for the health of a growing youth. 

Relation of muscles to proper posture. An erect posture 
and graceful carriage not only add to pleasing appearance 
but are important in maintaining the health. Round 
shoulders and stooping position decrease the capacity of 
the chest and interfere seriously with the action of its organs. 
It is important that boys and girls acquire a good posture 
early in life and that they realize that this is largely a matter 
of muscular training. In standing (111. p. 566), the head and 
body should be erect, the heels brought close together, and 
the shoulders brought into such a position that the back is 
approximately flat. In sitting, care should be taken not to 
bend the body over the desk, and a proper relation between 
the height of the chair and that of the desk should be secured. 

Permanent curvature of the spine frequently results from 
carrying loads of books or other heavy objects on one side 
of the body only ; pupils should therefore train themselves 
to use the arms alternately for this purpose. 

QUESTIONS AND APPLICATIONS 

1. What are four functions of the human skin? Show the adapta- 
tions of the skin for performing each of these functions. 

2. In what ways does the epidermis differ from the dermis? How can 
you prove each of your statements ? 

3. Give as many reasons as you can why frequent bathing is neces- 
sary. Name three kinds of baths. Give the special advantages of each. 



CONTROL OF OUR BODIES 569 

4. What directions should be followed in properly caring for the hair 
and the nails ? What is the reason for each direction ? 

5. Give specific directions for the treatment of burns. 

6. How is the normal temperature of our bodies maintained ? Discuss 
the effect of alcoholic liquors on the body temperature. 

7. Name three functions of the human skeleton. Show how the struc- 
ture of the skeleton adapts it for each of these functions. 

8. Distinguish between fractures, dislocations, and sprains. What 
treatment should be given in each of these accidents ? 

9. What is the difference between motion and locomotion of living 
things? Give illustrations showing to what extent each of these terms 
apply to various types of animals. 

10. What peculiar property has muscle tissue ? Show why this tissue 
is so important in the human body. 

11. What two types of muscle tissue have we? Where is each found 
in our bodies ? How is each controlled ? 

12. Describe the action of the biceps and of the triceps muscle. Con- 
tract both of these muscles at the same time and state the result. 

13. Name four conditions that are necessary for the healthy activity of 
the muscles. Describe in detail how you can supply each of these require- 
ments. 

14. Compare the relative advantages of gymnasium exercises and out- 
of-door sports. What are three advantages of vigorous exercise, other 
than that of developing the muscles ? 

15. Study the illustrations on pp. 566 and 567, and describe effective 
postures. How does a good posture tend to increase one's self-respect? 

PROBLEM 2. HOW ARE OUR BODIES CONTROLLED? 

Structure and Functions of Our Nervous System 

The human body as a collection of organs. In previous 
studies we have considered the digestive, respiratory, and 
circulatory systems of the human body, and we have seen 
how the organs of these systems furnish all parts of the body 
with food and oxygen and take away the wastes. We have 
studied the process of oxidation whereby we keep warm and 
gain the power to do work. And, finally, we are familiar 



570 MAN AND HIS ENVIRONMENT 

with the fact that the bones and muscles are the organs that 
give support to the body and provide the machinery for all our 
motions. Thus we have learned that the body is composed 
of many organs, each with its special function or functions. 

Cooperation of the organs. A human being is more than 
a mere collection of working organs, for all the organs work 
together for the common good. This is what we mean by 
cooperation. Suppose we take a few instances from everyday 
experience to illustrate this cooperation. 

When food is taken into your mouth, the salivary glands 
pour out upon it an abundant supply of saliva. Now the 
food never comes in contact with the glands. How is it, then, 
that they send out their secretion at just the right time and 
in the proper amount ? 

If a blow is aimed at your face, your hands immediately 
fly up to ward off the threatened injury. If the attack were 
pressed and you were compelled to defend yourself, your 
heart would beat much more rapidly, you would breathe 
faster, and a flow of perspiration would become evident. 
During the contest certain feelings, for example that of 
anger, also would doubtless be aroused. What is the ex- 
planation of this cooperation among your organs? 

Three classes of activities of our bodies. The functions 
carried on by the body are for the most part directly or 
indirectly under the control of the nervous system. 1 For 
practical purposes these various activities fall into three 
groups, according to the amount of conscious attention 
required to perform them. 

1 To the teacher. Each student might be asked to make as complete a list as 
possible of the activities he has carried on through the help of the muscles, glands, 
sense organs, or brain during a period of twenty-four hours, both while awake and 
asleep. It will be well from these lists to develop, on the blackboard, a daily routine 
for a high-school student, attention being called to the hygienic significance of each 
act. Two or three recitation periods might be devoted profitably to this study. 






CONTROL OF OUR BODIES 571 

Group I includes our conscious, or voluntary, activities — 
those that require attention to perform them. As examples 
of these conscious activities we may mention the selection 
of the books needed for study, the sustained attention we 
must give in order to learn the lessons that have been 
assigned, and the choice of foods that we make at lunch time. 

Group II comprises the acquired, or habitual, activities — 
those that required attention at first but not at the present 
time. These activities are acquired by repeated perform- 
ance ; we call them our habits. Let us see, for example, 
how it becomes possible for the driver of an automobile to 
work his way safely through the crowded streets of a city 
with hardly a thought as to what his hands and feet 
are doing. When he took his first lesson, he had to learn 
how to grasp the steering wheel with his hands, to release 
the emergency brakes, to throw the clutch into neutral, to 
turn on the ignition, and to press on the self-starter — just 
to get ready to back his car out of the garage. All this re- 
quired a good deal of conscious direction on the part of his 
brain. Watch the skillful driver after years of experience. 
He starts his car, backs it, goes forward, accelerates or retards 
his speed, turns his wheel to avoid obstacles, minds the traffic 
signals, and even throws on the emergency brakes to avoid 
an accident, with never a thought as to what is the right 
thing to do, because by long practice each of these move- 
ments has become habitual. How fortunate it is for us that 
we can perform so many of the necessary duties of everyday 
life with never a conscious thought, for example, dressing, 
walking, writing, talking, eating, or playing a musical instru- 
ment. 

Group III includes those inborn, or involuntary, activities, 
like breathing, beating of the heart, secretion of glands, 
which never have required any conscious attention for their 



572 



MAN AND HIS ENVIRONMENT 



performance. Since all these functions were performed from 
birth practically as well as at the present time, we call them 

also inborn, or native, ac- 
tivities. 

Each of these classes of 
activities will be discussed 
more or less in detail later ; 
but before we can proceed 
further with our studies of 
nerve functions, we must 
get some idea of the struc- 
ture of our nervous system. 
General structure and 
action of the nervous sys- 
tem. The human nervous 
system is shown in outline 
on this page, as it would 
appear if viewed from the 
back. We see that the 
larger portion of the upper 
part of the head (cranium) 
is filled with the brain and 
that from the brain the 
spinal cord extends down- 
ward through a canal in 
the spinal column of the 
neck and trunk regions. 
Forty-three pairs of nerves are connected with the two nerve 
centers (brain and spinal cord) that we have just named. 
These nerves branch out to all parts of the body. 

In many ways our nervous system resembles a telephone 
exchange, the nerves corresponding in function to the wires, 
and the brain and spinal cord to " central." For example, 




The brain, spinal cord, and nerves of man 



CONTROL OF OUR BODIES 573 

while walking along the street, if our eyes light upon a shining 
white circular piece of silver, a " message " passes from the 
eyes along one of the pairs of nerves into the brain, and we 
say to ourselves, " Hello ! here's a dime ! " This part of the 
brain " central " switches over the connection to other parts 
of the brain. " Messages," or stimuli, are sent down the 
spinal cord and out along the various nerves that connect 
with the muscles of the arms and the legs. We stoop over, 
grasp the coin, and meanwhile experience a feeling of satis- 
faction at this piece of good luck. 

How activities are brought about by the nervous system. 
A hundred experiences of our daily life much like this might 
be described. Each one of them, on careful analysis, is 
found to consist of five more or less distinct but related parts, 
as follows : (1) some kind of stimulus must be received from 
the exterior of the body ; (2) an impulse must be carried in to 
nerve centers along certain nerves ; (3) the nerve centers 
must make more or less complicated connections; (4) some kind 
of stimulus must be sent out from the nerve centers along other 
nerves ; and (5) this impulse must act upon muscles, glands, 
or some other kind of organ of the body in such a way as to 
control the work of the given organ. 

Biologists have proved that the nerve threads, or nerve 
fibers, for incoming messages are entirely distinct from those 
that carry outgoing messages. To the nerves that carry 
incoming messages is given the name afferent (af 'er-ent, from 
the Latin, meaning to carry to), since they always carry 
stimuli to nerve centers (111. p. 574). Efferent nerves (ef'er- 
ent, from the Latin, meaning to carry from), on the other 
hand, are nerves that convey stimuli out from the nerve 
centers. To the parts of the nervous system concerned in 
making connections between afferent and efferent nerves is 
given the name adjustors. The cells on or near the exterior of 



574 



MAN AND HIS ENVIRONMENT 



Motor cell of-*.^.^ 
cerebral cortex 



Cell of cortex of 
cerebrum 



the body which receive messages of temperature, pressure, 
light, and sound vibrations and transmit these messages to 
the afferent nerves are known as receptors. On the other 
hand, the nerve endings in muscles or glands are known as 

effectors, because of 
the effect that re- 
sults from a nerve 
stimulus. 

Hence, in order to 
carry on each of our 
functions, receptors 
must transmit their 
impulses to afferent 
nerves, which bring 
the messages to the 
nerve centers. Here 
the adjustors switch 
over the message to 
the efferent nerves, 
which convey the 
stimuli to the effec- 




Connecting 
fibres 

Ganglia of 
mid brain 



Efferent nerve 
from cerebrum - 

Efferent nerve from 5 

spinal cord 



ri^ — Cerebellum 



— Afferent nerve 
to cerebrum 

— Afferent nerve 
to cerebellum 

— Spinal cord 



—Afferent nerve 
to spinal cord 



Section of brain and spinal cord 
Arrows show direction of nerve impulses (" messages"). 



tors. These, in turn, bring about the countless activities of 
heart, stomach, hands, and feet. 

Microscopic structure of the nervous system. We come 
now to a description of the cells of which the nervous sys- 
tem is composed. To Golgi, an Italian biologist, who pub- 
lished an important paper in 1873, we owe our first clear ideas 
of the real cellular structure of the nervous system. By the 
use of special staining fluids, he found out that most nerve 
cells are far more complicated than any other cells of the 
body. Like other cells, each nerve cell has near the center a 
cell nucleus. The cytoplasm, however, is extremely irregu- 
lar in form, and since its branching processes resemble to a 



CONTROL OF OUR BODIES 



575 



Den c/r ties 



considerable extent the trunk and branches of a tree, these 
processes are known as dendrites (den'drits, from the Greek, 
meaning tree). 

On this page we see one of these nerve cells with its den- 
drites and an additional process which does not branch so 
extensively, but which may extend for a considerable dis- 
tance from the cell body. This is known 
as the axon (ak'son), or axis-cylinder, 
process. At a short distance from the 
cytoplasm this process becomes inclosed 
within two layers of material, which 
probably act more or less like the in- 
sulations or coverings that inclose tele- 
phone wires, to prevent the nerve 
stimulus from crossing over to another 
axon. The axon, after a longer or 
shorter course, finally ends in a muscle, 
a gland, or other organ in several termi- 
nal branches. 

So we see that nerve cells are ex- 
tremely irregular in shape, due to the 
fact that the cytoplasm extends out- 
ward in the form of branching den- 
drites, and also in the form of an axon 
with its terminal branches. All these 
extensions of the cell body bring a nerve cell into relations 
with other nerve cells or with other parts of the body. To 
the whole nerve cell with all of its processes, including the 
axon, is now given the name neuron (nu'ron). 

Nature of nerve stimuli, or impulses. We have likened 
nerve fibers to telephone wires, and nerve stimuli, or im- 
pulses, have been described as " messages " that pass along 
the axones. But in making these comparisons we must 




A nerve cell (neuron) 



576 MAN AND HIS ENVIRONMENT 

remember that telephony has, in all probability, little real 
resemblance to the action of the nervous system. In the 
first place, we know that the nerves of a frog transmit im- 
pulses at the rate of about 100 feet per second, which is about 
as fast as an express train travels when it is going 70 miles 
an hour. In man the nerve impulses travel about 270 miles 
an hour. An electric current, on the other hand, is trans- 
mitted thousands of miles per second ; hence, a nerve 
impulse cannot very closely resemble a telephone " message," 
at least in speed. We must admit our ignorance as to the 
real nature of nerve stimuli ; and we are still in doubt as to 
just what takes place in nerve cells after " messages " are 
received. No scientist has any idea as to how conscious- 
ness, feelings, and volition, or " will power," can arise as a 
result of nervous activity. 

Control of the inborn, or involuntary, activities of our 
bodies. On page 577 we see represented a lengthwise sec- 
tion of the human body with the heart, the diaphragm, and 
one kidney faintly outlined. Along the side of the spinal 
column, we observe a series of little enlargements connected 
with each other by nerve fibers. These are also connected 
with the nerves that run off from the spinal cord. Each of 
these little enlargements is known as a ganglion (plural, 
ganglia). A similar string of ganglia is also found on the 
other side of the spinal cord, although not shown in the 
picture. It is these ganglia, or tiny nerve centers (sub- 
stations), that control the organs of circulation, digestion, 
excretion, and other involuntary activities. Since these 
organs to which we have just referred apparently work with- 
out any conscious control on our part, the name autonomic 
(o'to-nom'ik, from the Greek, meaning self -regulating) has 
been given to the part of the nervous system that we are 
now describing. 



CONTROL OF OUR BODIES 



577 



An interesting series of experiments was carried on by Dr. 
Cannon of the Harvard University Medical School, which 
shows the action of the autonomic system of ganglia. A cat 
was fed with milk. It was purring contentedly ; and when 
one looked through an instrument known as the fluoroscope 
(floo-or'o-skop), one could see within the body the rhythmic 
contraction of the 
walls of the cat's 
stomach and intes- 
tines. Dr. Cannon 
then allowed a dog 
to come into the 
laboratory and to 
stay long enough to 
give a sharp bark. 
As soon as the cat 
heard this noise, it 
ceased to purr ; and 
on looking through 
the fluoroscope, one 
could see that all the 
contractions of the 
stomach and the in- 
testines had ceased ; 

in Other words, a Autonomic nervous system 

serious case of indigestion had set in. Often the action of 
the muscular walls did not start up again for half an hour 
or more following the fright or anger that the cat had 
experienced. 

A practical lesson which one can learn from the experi- 
ments is that, if we wish to carry on digestion properly, all 
topics that would tend to cause worry or anger should be 
ruled out of discussion while we are at the table or while we 




578 



MAN AND HIS ENVIRONMENT 



are digesting our food. The various emotions that we have, 
therefore, affect the autonomic ganglia, which in turn act upon 
the organs of digestion, circulation, and other involuntary 
activities. 

Structure of the spinal cord. The spinal cord extends from 
the base of the brain downward inside the spinal column. 
It gradually tapers off to a point in the region of the middle 



Afferent 



X^fS' to sp/na/ cord 



Gray 
/natter 




nerves 



Gang/fon ce//s 
'/on dors a/ roots 



\ - Sp/na/ ner ve 



Wte 

/natter \ / ^V"^ l ; ^ 'v¥\ / '"/"fftL ^ Afferent nerve 

to bra/n 

i*>^ Efferent nerves 
from sp/na/ cord 

7 T erm/na/ brushes 

Cross-section of spinal cord 
Arrows show direction of nerve impulses (" messages ")• 

of the back. When we look at a cross section of the spinal 
cord (111. above), we find that it is nearly divided in half. 

In the interior of the cord is a region shaped more or less 
like a capital letter H. This consists of gray matter, and 
inclosing the gray matter is the white matter. Connected 
with the gray matter on either side are the nerve fibers that 
form the various spinal nerves. It has been stated that these 
nerve fibers are of two kinds : those which carry messages 
into the spinal cord (afferent) and those carrying the mes- 
sages out from the spinal cord (efferent). 

Reflex action through the spinal cord. We can perhaps 
make clear how this nerve machinery acts by considering a 
simple experience like that which all of us have had when 



CONTROL OF OUR BODIES 579 

unexpectedly we touched a hot object like a stove. We know 
that the hand is instantly withdrawn, and that, too, without 
any conscious thought on our part, indeed even before we 
feel the burn. This is due to the fact that the receptors in 
the skin, having been stimulated by the heat, transmit the 
stimulus through the afferent nerves to the gray matter of 
the spinal cord, where the neurons are located. Here a 
connection is made with the efferent nerves, and the stimu- 
lus is immediately transmitted by these nerves to the effec- 
tors in the muscles. The muscles contract, and the hand is 
removed from danger. This kind of action is known as a 
reflex action. It consists of an incoming stimulus, a connec- 
tion made in the spinal cord, or " central," and an outgoing 
message to the contracting muscle. A great many of the 
activities of the body (e.g. the unconscious winking of the 
eyes) are reflex. 

Messages to the brain through the spinal cord. In addi- 
tion to its function in connection with reflex action, the spi- 
nal cord sends messages to the brain (111. p. 578). In the 
experience of touching the hot stove to which we have just 
referred, only when the messages reach the brain do we 
become conscious that we have been burned. The brain 
can also send messages through the spinal cord to the arms 
or the legs, that may cause these organs to move. All the 
messages referred to in this section are carried through the 
white matter of the spinal cord. 

Structure of the human brain. Let us now study a side 
view of the brain as it appears when the skull has been re- 
moved (111. p. 580). The largest portion of the brain, cere- 
brum (ser'e-br&m) , consists of the two cerebral hemispheres 
(the right one is shown in the figure). Below the cerebral 
hemispheres is the cerebellum (ser'e-bel'#m). We notice 
that the outer surface of the brain consists of a number of 



580 



MAN AND HIS ENVIRONMENT 



elevations, or convolutions, which look more or less like a suc- 
cession of irregular mountain ranges. Between these con- 
volutions there are depressions, or valleys, which are known 
as fissures. 

In the brain the gray matter is on the outside, and not 
towards the center, as was the case in the spinal cord. Since 



Cerebral 
hemisphere 




Cerebellum ' 

Medulla s 
oblongata 

Spinal - " 
cord 



" v Spinal nerve 
Surface view of brain and spinal cord 

gray matter, wherever found, is always composed of the 
bodies of the nerve cells, it is evident that the outer surface 
of the brain, and consequently the number of nerve cells, is 
considerably increased in extent by this succession of con- 
volutions and fissures. It is this tremendous increase in the 
number and complexity of the nerve cells in the human 






CONTROL OF OUR BODIES 



581 



brain that places man high above all other animals in 
intelligence. 

Different parts of the brain are set apart for special func- 
tions. The surface view of the brain (111. below) shows certain 
areas that are labeled. For instance, in the rear of the 
brain the center of vision is evidently located. Hence the 
nerves that bring in the messages from the eyes must finally 
bring their messages 
to this region of vision 
in the cerebral hemi- 
spheres. In a similar 
way the nerves from 
the ears carry their 
stimuli to the side 
region of the brain 
marked hearing . 
Along the side of the 
brain, too, are the re- 
gions of the cerebral 
hemispheres that con- 
trol the muscles of the leg, arm, face, lips, tongue, and organs 
of speech. These facts we have just stated have been 
proved by long series of experiments upon animals and by 
observations of diseased conditions of the brain among 
human beings. 

Connections from one part of the brain to another. On 
page 574 we have represented a very few of the possible lines 
of connection from one part of the brain to another. These 
connections are brought about by nerve fibers that run 
from one convolution to another (111. p. 575) or from the 
convolutions of one cerebral hemisphere of the brain to those 
in the other hemisphere. No telephone system in all the 
world is so complex in its connections as are the possible 




Surface view of brain 
Showing localization of functions. 



After Williams 



582 MAN AND HIS ENVIRONMENT 

connections between the various cells of our nervous system. 
By means of these connecting fibers we are enabled to do the 
complicated acts which it is possible for an intelligent human 
being to accomplish. It is estimated that there are ten 
billions (10,000,000,000) of nerve cells within the gray matter 
of the brain alone. Is it any wonder, then, that it takes us so 
long to learn how to perform some of the complicated acts 
which we finally learn? How fortunate too that, when once 
we have trained ourselves to walk, or to dress ourselves, we 
can then carry on these habitual activities while giving atten- 
tion to other matters. 1 

Upon what our conduct depends. If we study carefully 

the illustration on this page, we ought to learn many valu- 

^ mm able lessons. Let us 

Imputses over <6 V Imputses of ,1 , 1 

association paths*>*^t \^^^ visua/ origin SUppOSe tnat a DOy IS 

/ er \ near a fruit stand. 

motor ■ 

\ centre ! " Impulses of visual 

'*\ imposes of o ri g in " come into his 

auditory origin brain as he sees an 

orange he would like 

Motor imputses 

After suies to eat. The tempt a- 

Diagram to illustrate conduct . . , . 

tion is increased by 
" impulses of auditory origin," when he hears another boy 
whisper to him to take the orange. Were this all of his 
experience, his " cerebral motor center " (i.e. his brain) thus 
appealed to would doubtless send out " motor impulses," 
and the youth would seize the orange. 

Fortunately, however, " deterrent impulses," which would 
tend to hold the boy back, are quite likely to act upon him. 
For example, he is quite likely to remember that the orange 
does not belong to him. He may think of the shame that 
would come to himself and to his family if he were caught 

1 For further discussion of habits, see pages 621-624. 



Deterrent y^ 
impulses 



V 



CONTROL OF OUR BODIES 583 

stealing. And so, let us hope, these deterrent impulses 
together with " impulses over association paths " (namely, 
" will power ") will cause his cerebral motor centers to send 
out motor impulses that will take him out of the reach of 
temptation. 1 

The Sense Organs of Our Bodies 

Structure of the eye. Like the rest of the nervous system 
the eye is a marvelous mechanism, which enables us to 
acquire a wide range of knowledge of our environment. 
These organs are nearly spherical in shape, and are well pro- 
tected within the bony sockets of the skull and by the eye- 
lids which move over them in front when they are in danger. 
By studying a section of the eye (111. p. 584) we note 
that it is covered on the outside by resistant sclerotic (skle- 
rot'Ik) coat. If we look in a mirror and pull back the eye- 
lid, we see that this coat is white, except at the bulging 
front region where the cornea (kor'ne-d) is transparent. 

Inside the sclerotic is the choroid (ko'roid) coat, richly 
supplied with blood vessels and with a black pigment much 
like that found in the pigment spots in the skin. In the 
front of the eye the choroid coat is visible as the colored part, 
namely the iris (I'ris), in the center of which is an opening 
known as the pupil of the eye. By means of tiny muscles 
the size of this opening can be regulated in such a way as to 
allow a small or a large amount of light to enter. 

The most wonderful layer of the eye is the inner coat or 
retina (ret'i-nd). It consists of countless neurons (recep- 
tors) which are acted upon by the rays of light. These rays 

1 As a result of general discussion of this diagram, the class can doubtless make 
other practical applications of the principles that determine right and wrong con- 
duct. For instance, what determines whether a given boy will or will not cheat in 
examinations? Whether a soldier will be a coward or a hero in time of battle? 



584 



MAN AND HIS ENVIRONMENT 



are focused on the retina by the action of the crystalline lens. 
This can be altered in shape so that we are able (if our eyes 
are normal) to see clearly the distant horizon or objects 
within a few inches of us. 

Action of the eye. We can, perhaps, better understand 
the action of the eye if we compare it to a camera. In 
both there is an opening through which light can enter, the 
size of which can be regulated by an iris (diaphragm). Both 




Film 

corresponding 

to retina. 



Diaphragm, 
corresponding 
to iris^ 
Opening 
corresponding 
to pupil 



Cornea - 



Ciliary -^ 
muscle 



Yellow 
-spot 

— Retina 
Choroid 
-Sclerotic coat 



Lens- 




Section of the eye and a section of a camera 
How do the methods of focusing in the eye and a camera differ ? In what respect is 
the iris like the diaphragm and in what respect is it different ? What is the pupil ? 

are lined with black surfaces. In both there is a lens which 
focuses the light rays so as to secure a clear picture. In the 
camera, however, the lens is moved forward or backward in 
focusing, while in the eye the same result is secured by 
changes in the convexity of the lens. In both the eye and 
the camera the " picture " is formed at the back on a sen- 
sitive surface. In the camera it is the film which receives 
the impressions, and the picture must later be developed by 
the action of chemicals. In the eye, on the contrary, the 
light stimuli are at once conveyed by the fibers of the optic 



CONTROL OF OUR BODIES 



585 




nerve to the visual area of the brain, and it is there that we 
become conscious of seeing. A moment's thought will make 
clear to us that our sight impressions of past times are some- 
how stored up as more or less definite memories of what has 
been seen before. 

Defects of the eyes. A normal, healthy eye has the 
power of adjusting itself so that objects become visible which 
are within five to ten inches or 
as far away as a distant horizon. 
Many people, however, find that 
they can see objects near at hand 
much more clearly than objects at 
a distance ; in other words, these 
people are nearsighted; others, on 
the other hand, are farsighted. 
These defects in vision are due to 
imperfect formation of the eye and 
can be corrected only by the use 
of proper eyeglasses or spectacles. 
Glasses should be purchased only on the recommendation 
of a competent eye specialist. 

Another very common defect of the eye is known as astigma- 
tism. Many people, on looking with each eye separately at 
the illustration above, find that some of the radiating lines 
stand out sharply defined, while others are indistinct or 
blurred. In reality, all the lines are equally distant from 
each other, and the indistinctness referred to above is due 
to the fact that some of the rays of light are not brought to 
a focus. Astigmatism, like nearsightedness and farsighted- 
ness, should be corrected by the use of proper glasses ; other- 
wise constant eyestrain is likely to cause headaches and other 
disorders of the body. 

Some people, too, are unable to distinguish clearly various 



Test for astigmatism 

Do all these lines look to you to 
be equally clear ? 



586 MAN AND HIS ENVIRONMENT 

colors ; thus red and green may appear the same to them. 
In other words, such people are color blind. Color blindness 
cannot be corrected by glasses but may be, to some extent, 
by training. 

Care of the eyes. The eyes have, as we know, wonderful 
powers of adapting themselves to varying conditions. This 
adaptability often leads us to abuse them. Thus we fre- 
quently read when the light is insufficient, we look steadily 
at objects until we suddenly find that we cannot see clearly, 
and we read or study while riding in swiftly moving trains. 
In these and other ways we compel our eyes to make adjust- 
ments under trying conditions, and more or less severe eye- 
strain is sure to result. 

When we read, we should make sure that the light is 
sufficient and steady. When we write, it should come over 
the left shoulder. The type on the printed page should be 
of adequate size and clearness ; the lines should not be close 
together, and the paper should not have a glossy surface 
to reflect the light into the eyes. One should remember 
too that the eyes, like other organs of the body, need 
frequent periods of rest. Hence study hours should be 
followed by periods in which the eyes are allowed to relax. 
Pupils who have defective eyesight should secure proper 
glasses. 

Structure and functions of the ear. The human ear is 
likewise a very complicated and remarkable organ. Three 
parts or regions may be distinguished ; namely, the outer ear, 
the middle ear, and the inner ear. A study of the diagram 
(see illustration) shows us that the outer ear consists not 
only of the cartilaginous (kar'ti-laj'i-n#s) part that is 
visible at the side of the head, but also of an auditory canal 
which extends inward through the bone of the skull. The 
inner end of this canal is closed by a thin membrane, the 



CONTROL OF OUR BODIES 



587 



tympanum (tim'pd-num) called also the eardrum, but more 
accurately the drumhead (111. below). 

The middle ear is seen as a very small cavity which is con- 
nected with the throat by the Eustachian (u-sta'ki-dn) tube. 
Across the cavity of the middle ear extends a chain of three 
tiny bones (the smallest in the body), known from their 
shape as the hammer, the anvil, and the stirrup. The base 



Semf- Cir cu/ar 
Cana /s 



Auditory_ 
Canal 



Middle Ear 
with Bones 




Auditory 

Nerve 



Cochlea 



Eustachian 
Tube 



Diagram of the principal parts of the ear 

of the stirrup is attached to another thin membrane which 
shuts off the middle ear from the inner ear. 

The inner ear, like the retina of the eye, is by far the most 
complicated part of our auditory apparatus. It consists of 
three semicircular canals, arranged at right angles to each 
other, which help us to keep our balance. There is also a 
spiral canal known as the cochlea (kok'le-d) . All these canals 
are filled with a liquid and their inner surfaces have count- 
less receptors which send messages through the auditory 
nerves to the region of the brain in which is located the func- 
tion of hearing. (See 111. p. 581.) 

When sound vibrations enter the tube of the outer ear, 
they cause the tympanum to vibrate, and these vibrations 



588 MAN AND HIS ENVIRONMENT 

are transmitted across the middle ear by the chain of tiny 
bones. The inner membrane thus set in motion stimulates 
the neurons within the semicircular canals and the cochlea. 
The " messages " are then transmitted to the brain and we 
become conscious of our position in space and of various 
sounds. Like the " pictures " that are recorded in the vis- 
ual area of our brains, the sound " records " become more or 
less permanent ; for we can remember the music or the voices 
of friends we heard yesterday, or even those of years ago. 

Care of the ears. In case the outer ear is frozen, it should 
be thawed out slowly by the application of snow or ice. 
The external ear and the auditory canal (111. p. 587) should be 
kept clean and should be thoroughly dried, especially after 
bathing. If ear wax accumulates, it should be removed by a 
doctor ; do not try to do it yourself. In case a foreign body 
gets into the ear canal, do not get excited or try to remove it 
without help from a doctor ; more harm often results from 
the effort to remove the obstruction than from the object 
itself. If an insect crawls in, a little warm water or sweet oil 
gently dropped in will usually remove it, or a light held near 
the ear will attract it and cause it to crawl out. The advice 
given by an old doctor is wise advice : " Never poke anything 
into your ear or scratch it with anything but your elbow ! " 

In blowing the nose only one nostril should be closed at a 
time, and care should be taken not to blow too violently, 
since germs and mucus may be forced from the throat cavity 
up the Eustachian tube (111. p. 587) into the middle ear, 
thus causing infection of the middle ear. For a similar 
reason, after spraying the nose, liquid should not be snuffed 
up too violently ; it should be allowed to run out, and five 
minutes should elapse before blowing the nose. 

Earache may be caused by a cold or by the closing of the 
Eustachian tube. A hot-water bottle or an electric pad 



CONTROL OF OUR BODIES 589 

should be held over the outer opening of the ear. Soft food 
should be eaten, and a rest should be taken. If pain con- 
tinues, a physician should be consulted. Do not use lauda- 
num or any patent medicine. Consult an ear specialist in 
case of any ear trouble. 

Running ear is caused by the discharge of pus from an 
inflamed middle ear, the drum having been perforated by the 
pressure of the liquid trying to force its way out. This often 
is a result of colds or of adenoids. A gathering in the ear is 
an accumulation of pus in the middle ear that cannot escape 
by way of the Eustachian tube because it has become clogged 
up. If a gathering in the ear or a running ear is neglected, 
the poisonous material may work its way inward and cause 
mastoiditis (mas'toid-i'tis), which is an infection of the 
mastoid cells in the bony projection that is felt on the skull 
back of the outer ear. Repeated perforations of the drum- 
head may result in deafness. Temporary deafness may also 
be due to a closing of the Eustachian tubes. 

Sensations of touch, taste, smell, and pain. All over the 
body, as we learned in our study of the skin, are numberless 
receptors which transmit to the brain the stimuli that result 
in sensations of touch. These receptors are best developed 
in the lips and the tips of the fingers, and they become won- 
derfully efficient in those who have lost their sight, as we shall 
see later on. (See 111. p. 612.) 

In the lining of the nose are other receptors that are acted 
upon by stimuli of a gaseous nature. When these " mes- 
sages " reach the cells of the brain we become conscious of 
odors. The tongue and the palate are well supplied with 
still other neurons that transmit to the brain impressions of 
taste. We know by experience that there are receptors that 
send into the brain stimuli that make us conscious of pain, 
either because of injuries on the exterior of the body or of 



590 MAN AND HIS ENVIRONMENT 

derangements within. When all is well, these various sense 
organs we have been describing give us great enjoyment ; 
in times of danger they supply us with needed warnings. 

Hygiene of the Nervous System 

Conditions necessary for a healthy nervous system. In 

studying the hygiene of other parts of the body, we found 
that four conditions are always necessary for healthy activity. 
That the nervous system too may develop as it should and 
that it may do its work properly, the same four conditions 
are essential ; namely, proper food, abundance of fresh air, 
varied forms of activity, and periods of rest. Let us now 
consider each of these conditions somewhat in detail. 

Food and air. In the nervous system of man there are un- 
counted billions of nerve cells. Each of these cells must be 
supplied with nutritious food and pure air, or it becomes 
stunted in its growth and unable to do its proper work. 
Each of these busy cells is constantly giving off carbon 
dioxid, water, and other wastes ; and if these are not re- 
moved from the body and fresh oxygen supplied, one feels a 
drowsiness and headache and is unable to think clearly. 
Well- ventilated rooms, both by day and by night, are of 
prime importance in the hygiene of the nervous system. 

Varied activity and rest. To develop a well-balanced brain 
one must be active along many lines. Experience tells us 
that we cannot work successfully at the same task hour 
after hour without some change. This is due to the fact 
that through continuous activity of a given set of neurons 
they become clogged with waste matters. Hence they can- 
not function properly until these wastes have been elimi- 
nated. Therefore, varied activity is an important principle 
in sound education. The young child must, of necessity, 
turn, after a short time, from one lesson to another, and 



CONTROL OF OUR BODIES 591 

all lessons must finally give way to the relaxation of play. 
Unfortunate is the boy who fails to find exhilaration in 
baseball, bicycle riding, or general athletics ; for these sports, 
when properly regulated, besides developing strong lungs 
and vigorous muscles, are important means of educating the 
nerve cells and fibers. 

Not only in youth, but throughout life, the student, the 
business man, or the laborer, at the end of a day's employ- 
ment must find relaxation in other forms of activity. If he 
fails to do this, he will become weary of his work and he will 
also finally lose the power of enjoying the pleasures he has 
been neglecting. Tired nerve cells can be restored by rest 
alone. In childhood and youth an abundance of sleep is 
absolutely essential for healthy development. Late hours 
of evening entertainment or of study should never be allowed 
to keep growing boys or girls from having at least nine hours 
of sleep. 

What is meant by drugs, stimulants, and narcotics ? It is 
important, at the very beginning of our discussion, to keep 
clearly in mind that by a drug we mean not only those 
compounds contained in medicines, but also any substance 
tending to have an abnormal effect on the body, either by 
increasing its activity (stimulants), or by decreasing or de- 
pressing activities (narcotics). Tea and coffee, for example, 
are often taken to drive a weary nervous system to action. 
Instead of a stimulating whip of this kind, rest and proper 
food would be far better and more effective. Other sub- 
stances, such as morphine, opium, cocaine, and nicotine, 
produce results just the opposite to that of stimulants ; that 
is, they cause a depressing or narcotic effect. In spite of 
the apparently stimulating effect of the moderate use of 
alcohol, this substance is now universally believed by 
physiologists to belong in the group of narcotics. 



592 MAN AND HIS ENVIRONMENT 

Drugs and medicines are of two kinds : (1) those used for 
the lesser ailments and other routine purposes, such as 
throat gargles, cathartics, and tincture of iodine for cuts; 
and (2) a limited number of narcotic drugs which should 
never be used except in the most acute emergencies, and then 
only under the doctor's orders. Whereas an individual 
user of alcohol may or may not become a slave to it, anyone 
who experiments with a narcotic drug such as cocaine, 
morphine, opium, heroin (he-ro'm), or hashish (hash'esh) 
may become enslaved to it, and probably will. In most cases 
drugs are unnecessary except when prescribed by a repu- 
table physician in cases of illness. Indeed, they frequently 
do a great deal of harm, as is often the case with cocaine, 
morphine, and alcohol. 

In the first place, drugs are often taken to get rid of 
weariness, pain, or mental suffering. Instead, the victim 
should seek to remove the cause of the difficulty. Pepsin 
tablets, for instance, may be used to relieve indigestion. 
However, they surely do more harm than good if we fail to 
get at the real cause of the discomfort. It is most dangerous, 
too, for a person to rely on sleep-producing drugs ; he should 
rather remove the troubles of body and mind that induce 
the sleeplessness. 

Again, those who employ narcotics like cocaine, opium, 
tobacco, or alcohol are in grave danger of becoming slaves 
to these substances, and to find that an increase in the 
quantities of the drugs is necessary to satisfy their cravings. 
" The hygienic ideal to be striven for is a robustness of life 
which shall make alcohol superfluous as a relish, food, or 
drug, and a cheerful, active mind which needs no artificial 
aid to keep it hopeful and sympathetic. The attainment 
may not be an easy task. Grief and worry and overwork 
may be added to an original depression of temperament, but 



CONTROL OF OUR BODIES 593 

the use of alcohol is never more unsafe than when sorrows 
are the excuse, and never so selfish and cowardly as when the 
motive is to shun responsibilities that ought to be faced." x 

In the third place, the use of drugs, even of stimulants like 
tea and coffee, by the young should be regarded as quite 
unnecessary, and probably harmful. Growing protoplasm 
is very sensitive to stimulants and narcotics, of any kind. 
These substances are not needed by young people in health, 
and if used to any considerable degree, they tend to inter- 
fere with the normal development of the nervous system and 
of other parts of the body. More than this, if drugs are 
needed later in life in cases of illness, they will prove less 
effective if the body has already become accustomed to their 
action. 

What is the truth regarding the effects of alcohol? " Re- 
spect for the truth, I take it, is the most vital characteristic of 
an individual life as it is of a nation's life." 2 Throughout 
this textbook we have emphasized the importance, in seeking 
the truth, of basing all conclusions on known facts. We have 
tried to make clear the methods by which scientific facts 
have been slowly demonstrated, how tentative laws have 
been developed, and how these laws have been modified as 
new facts have been ascertained. It is evident, therefore, 
that what may have been regarded as scientific truth by one 
generation may not be so regarded by the next. In dis- 
cussing the effects of alcohol in this and in later sections, we 
shall follow the same plan, and try to point out some of the 
scientific facts relating to alcohol and how these facts have 
been ascertained. 

1 From Nutritional Physiology, by Percy G. Stiles, Assistant Professor of 
Physiology in the Harvard Medical School. Used by permission of W. B. Sanders 
Company, Publishers. 

2 Dr. Edward J. Goodwin, formerly Assistant Commissioner of Education in 
charge of all the high schools of the State of New York. 



594 MAN AND HIS ENVIRONMENT 

The question of the use of alcohol is a many-sided one. 
It has to do not only with physiological effects, but also 
with social and economic relations. Any legislation look- 
ing towards the limitation or control of the use of intoxicat- 
ing drinks can justly be based, not upon the right of govern- 
ment to set standards of personal morality, but rather upon 
its right to make the laws needed to protect its citizens. The 
mind of man has struggled with the alcohol problem for 
centuries. The very fact that the use of alcoholic liquors 
has presented a problem for human beings all through these 
centuries shows that it is not only a complicated question, 
but also that it is one of a serious nature, and that it is world- 
wide. Unfortunately, this problem has become so seriously 
complicated in recent years that it is exceedingly difficult to 
carry on a discussion of alcohol in a scientific spirit. 

Dr. Reid Hunt, Head of the Department of Pharmacology 
of the Harvard Medical School, who is recognized as an 
authority throughout the world, writes the authors as follows : 
" I have been accustomed to the moderate use of alcoholic 
liquors. I am, however, perfectly willing to forego the use 
of alcoholic liquors as long as I remain in the United States, 
(1) because I believe in obeying the law, and (2), and more 
especially, because of the dangers that arise when alcohol 
is used by locomotive engineers, drivers of automobiles, and 
others who are responsible for human lives in this machine 
age. The Brotherhood of Locomotive Engineers, under the 
leadership of Chief Stone, years ago, on their own initiative, 
entered into an agreement to refuse membership to those 
who use alcohol. It is a well-known fact that alcohol slows 
down nervous reactions. Individuals, however, differ so 
much in their reaction to alcohol that it is impossible to lay 
down a scientific definition as to what is meant by moder- 
ation in the use of alcohol. The long experience of the 



CONTROL OF OUR BODIES 595 

human race with alcoholic drinks shows that what may be 
true of one individual may not be at all true of another. 
Hence any experimentation with alcoholic liquors, espe- 
cially by young people, presents grave dangers. Morphine, 
opium, and hashish are drugs that are consumed by the 
individual all by himself, in his desire to get away from 
his immediate environment. Alcoholic liquors, on the other 
hand, are almost always social beverages, and those who 
drink them usually seek the companionship of others, 
with the consequent danger of taking an immoderate 
amount." 

Dr. Thorne M. Carpenter, of the Nutrition Laboratory of 
the Carnegie Institution of Washington, states that long 
experimental studies in their laboratories show that even the 
moderate use of alcohol results in a distinct loss of human 
efficiency. " To sum up, alcohol is rapidly and completely 
absorbed in the digestive tract, the rapidity of absorption 
depending on the amount, concentration, and presence or 
absence of food. It is carried to all parts of the body, and 
appears in the blood, urine, and the breath. ... An ounce 
of alcohol (two tablespoonfuls) . . . will render an individ- 
ual less efficient for at least two or three hours." 1 

Many other experts have studied the effects of the use 
of alcohol upon the human organism, and many opinions 
have been expressed as a result of these studies. No one 
has attempted to deny the dangers attending the use of 
alcohol, especially as a habit-forming beverage, and the 
damage which its immoderate use does to the individual and 
to a nation. Even those who seem to see little harm in 
moderate drinking are ready to admit that a considerable 
number of moderate drinkers at times become immoderate. 
Sometime or other they are likely to be betrayed into drink- 

1 Public Lecture, Harvard Medical School, February 14, 1932. 



596 MAN AND HIS ENVIRONMENT 

ing to excess, with resulting danger of disastrous consequences 
to themselves or to others. 

It seems to be true that certain nationalities are able to 
use alcoholic beverages with more moderation than others. 
Here in America, however, we are likely to go to extremes, 
as witness the saloon which depended for its financial success 
upon a lack of moderation on the part of its patrons. It 
came to be a menace not only to the physical but also to the 
economic welfare of our people. 

" I think the truth should be told as nearly as one can 
get at it ; but I presume that so far as the physiological effects 
alone are concerned it will be difficult to get at the truth, 
and very difficult to make general statements that will apply 
everywhere, since individuals react so differently to the 
physical effects of liquors. The great argument with refer- 
ence to liquor is, of course, its habit-forming propensity 
and the social consequences. We do need to get back to 
the teaching of temperance and self-control and to rely 
upon education and persuasion rather than on coercion 
and law." x 

True, by no means all recognized authorities are willing 
to maintain without qualification that the use of alcohol in 
moderate quantities by adults is always harmful. There is no 
denying the fact, however, that alcohol is in a different class 
from the other narcotics, and that a far larger element in 
society uses this drug than any other. It must also be ad- 
mitted that a considerable proportion of these users are able 
to restrain their appetites and to be reasonably moderate on 
most occasions. Admitting all that has been said, we are 
sure youth ought to have impressed upon it the grave dan- 
gers it is sure to encounter from any use of alcohol, at least 
until the period of maturity. 

1 Dr. Harry Emerson Fosdick, Minister of the Riverside Church, New York City. 






CONTROL OF OUR BODIES 597 

Alcohol and athletics. 1 " Every schoolboy knows the re- 
markable record made by the Philadelphia Athletics under 
the leadership of ' Connie Mack.' This widely known base- 
ball manager says he wouldn't bother with a youngster who 
drinks. He believes that alcohol prevents ' clean living and 
quick thinking/ and this is how he persuades his men to ab- 
stain. ' I make my appeal from four different sides. First, 
from the standpoint of the public — the people who pay to 
see good baseball. They are entitled to see the player at his 
best, not slowed up by drink. Second, from the standpoint 
of the club. The player gets a good salary, for which he 
owes his best services. I say that the man who doesn't do 
his best is dishonest with the club. The third appeal is from 
the standpoint of a man's fellow players. It isn't fair to 
the other members of the team to have one important part 
of the baseball machine ' going bad,' as they say. Fourth, 
I put it straight up to the man himself, that he isn't giving 
himself a fair chance. I find that in one of these four ways 
I can get to a man.' " 

" In football Amos Alonzo Stagg, [formerly] of the Uni- 
versity of Chicago (111. p. 598), has been for a long period of 
years the veteran of a clean game, and he writes as follows : 
1 As a coach I do not believe, and none of the coaches that 
train men believe, in the use of alcoholic beverages. I was a 
member of the coaching staff of the Olympic team in 1924, 
and alcohol was one of the forbidden things when we went 
over to Paris. . . . The coaches and trainers generally are 
dead against the use of alcoholic liquors in training, even 
beer.' " 

" Helen Wills Moody, long the tennis champion of the 
United States, declares that in playing tennis one glass of 

^rom Effects of Alcoholic Drinks by Emma L. Benedict Transeau. Used by- 
permission. 



598 



MAN AND HIS ENVIRONMENT 



beer is ' enough to make a difference in one's eye, coordina- 
tion, and balance. The precision that tennis demands,' she 
says, ' makes necessary total abstinence, even from beer.' " 

Effect of alcohol on the 
nervous system. " The 
effect of alcohol appears to 
be, as it were, to shave off 
the nervous system, layer 
by layer, attacking first the 
highest-developed faculties 
and leaving the lowest to 
the last, so that we find 
that a man's judgment may 
be lessened, though at the 
same time some lower facul- 
ties, such as the imagination 
and the emotions, may ap- 
pear to be more active than 
before. . . . 

" Alcohol . . . makes all 
the nervous processes slower, 
but at the same time it has 
the curious effect of produc- 
ing a kind of mental anaes- 
thesia, ... so that these 
processes seem to the person 
himself to be all quicker 
than usual, instead of being, 
as they really are, much slower. Thus a man, while 
doing things much more slowly than before, is under the 
impression that he is doing things much more quickly. 
What applies to these very simple processes applies also to 
the higher processes of the mind ; and a celebrated author 



f;#: 




v ,^. 


; " 


* 




#• 


^ 






,, -l.X 




mr 


jj \£k mk 




"'fii . 

Win 


1 

' HHH 




■.'■$mM 


WW m 




1 


mm m B|pl4/ 




1 




-,.,..«■**«/» 


■■-■: ' f 
, .f : ""' 


ii ' '' '.H 



Autographed for this book 

Amos Alonzo Stagg 
Former football coach of Chicago University 



CONTROL OF OUR BODIES 599 

once told me that if he wrote under the influence of a small 
quantity of alcohol, he seemed to himself to write very 
fluently and to write very well, but when he came to exam- 
ine what he had written next day, after the effect of the 
alcohol had passed off, he found that it would not stand 
criticism." x 

Alcohol and automobile driving. Alcohol is becoming 
more and more a menace to our safety, when we consider the 
pernicious effect of its use by those who drive automobiles. 
For instance, in the State of Massachusetts, in the year 1931, 
there were 40,597 recorded accidents due to the operation of 
motor vehicles. In these accidents 793 persons were killed 
and more than 48,800 were injured. Nearly one fourth of 
the total killed and injured were children. Many of the 
children and adults who escaped death were doubtless 
maimed for life. The Statistician of the Massachusetts 
Registry of Motor Vehicles makes a very conservative 
estimate that at least 5000 of the non-fatal accidents were 
due to the action of alcohol, and that it was a causative 
factor in the cases of 68 persons who lost their lives. In 
1931 5535 automobile licenses were revoked because the 
drivers were convicted of being under the influence of alco- 
hol. Doubtless there were many other cases of drivers who 
were potentially dangerous that escaped detection. Simi- 
lar statistics are found to be true in other states. The num- 
ber of motor cars on the public roads throughout the country 
has increased enormously, and even clear-headed drivers 
find more and more difficulty in escaping threatened injury 
or death. Too much emphasis, therefore, cannot be laid 
on the danger in the use of even a small amount of liquor by 
those who operate passenger cars and trucks. 

1 From Sir Thomas Lauder Brunton, Lectures on the Action of Medicine, pp. 190, 
191, 194. Used by permission of The Macmillan Company, publishers. 



600 MAN AND HIS ENVIRONMENT 

Final summary on the effects of alcohol. " In the fore- 
going pages we have stated the salient facts concerning the 
physiological action of alcohol and alcoholic drinks. It only 
remains to point out for the student the obvious conclusions 
to be drawn from the long and, on the whole, very sad 
experience of the race with alcoholic drinks. The first is 
that except in sickness and under the advice of a physician, 
alcoholic drinks are wholly unnecessary and much more 
likely to prove harmful than beneficial. The last is that 
their frequent, and especially constant, use is attended with 
the gravest danger to the user, no matter how strong or self- 
controlled he may be. . . . The only absolutely safe atti- 
tude toward alcoholic drinks is that of total abstinence from 
their use as beverages." l 

The Chemical Controls of the Body 

How the chemical control of the body was discovered. 

Not so many years ago, an account of the controlling agencies 
of the body would have begun and ended with a study of the 
nervous system and its functions. Such an account would 
now be considered incomplete even in an elementary text- 
book. In the case of the nervous system, as we have seen, 
control is brought about by means of impulses, or " mes- 
sages," that are sent out from the nerve centers through vari- 
ous nerve fibers to various organs of the body. These nerve 
centers may be caused to act by other messages that come 
in from the outside of the body through other sets of fibers. 
While the nature of these impulses is not as yet understood, 
their effects are well known. 

For over a hundred years it has been known that the 
nervous system is not the only means by which the varied 

1 From Hough and Sedgwick, The Human Mechanism, p. 370. Used by per- 
mission of Ginn and Company, publishers. 



CONTROL OF OUR BODIES 601 

activities of the organs of the body are stimulated and 
controlled. As a result of the careful work of many scien- 
tific investigators there has gradually been accumulated a 
great store of knowledge concerning a very different agency 
of control, which is called the chemical control. 

Chemical control in the action of the pancreas. You have 
learned that when the food from the stomach enters the small 
intestine, the pancreatic juice is poured out over it. This 
action was formerly supposed to be caused by messages 
through the nervous system sent to the pancreas. It is now 
known that this action on the part of the pancreas is due to a 
chemical messenger formed in tiny gland cells of the mucous 
membrane of the small intestine. When some of the food 
from the stomach is forced into the small intestine, it stim- 
ulates the formation of a chemical substance, secretin 
(se-kre'tin), which is absorbed by the blood and carried 
through the body till it reaches the cells of the pancreas. 
The pancreas, then, is caused to act by secretin carried to it 
by the blood from glands of the small intestine. 

How insulin is related to diabetes. You have doubtless 
heard of the disease diabetes (di'd-be'tez). One who has this 
disease cannot store or oxidize sugar. Consequently sugar 
accumulates in the blood to such an extent that it acts as a 
poison. Much of the sugar is then excreted by the kidneys. 
Recently it has been proved that this disease is caused by 
the failure of the pancreas (111. p. 93) to produce a chemical 
substance, which, when absorbed by the blood and carried 
to the liver cells, enables them to store up sugar. When this 
substance is absorbed by other cells like those of muscle, 
these cells are enabled thereby to oxidize the sugar. This 
chemical substance has been called insulin (ln'su-lm). 

During the year 1923, Dr. F. G. Banting of the University 
of Toronto devised a method of preparing insulin from the 



602 MAN AND HIS ENVIRONMENT 

pancreas of the sheep. When insulin is injected into the 
blood of a diabetic patient in this method of treatment, the 
patient is able to store and oxidize the sugar. The use of 
insulin must, however, be continued ; it is not a cure for the 
disease. 

What the internal secretions are. The secretin of the 
glands of the small intestine and the insulin of certain gland 
cells in the pancreas are examples of chemical substances 
that either alone, or with the aid of the nervous system, con- 
trol and regulate vital activities of the body. Since these 
secretions are absorbed by the blood and are not poured out 
through ducts upon some free surface, as are saliva and 
gastric juice, they are known as internal secretions, and the 
glands that form these chemical substances are known as 
glands of internal secretion. The substances that these 
glands secrete are also called hormones l (hor'monz, from the 
Greek, meaning exciting), because they excite the pancreas, 
the liver, and other organs to activity. 

But glands of internal secretion are not limited to those 
mentioned above. There are at least seven other glands 
which secrete one or more hormones ; each one has one or 
more functions. The following is a very brief account of 
three of these vital, wonder-working glands. 

Adrenal glands and adrenalin. The adrenals are small 
glands located near the kidneys (111. p. 603), as the name 
" adrenal " indicates. Until recent times these glands were 
neglected, since they were thought to be a part of the fat that 
was found in connection with the kidneys. A hormone, 
adrenalin (ad-re 'nal-in), has been obtained from the outer 
part of these glands. One of the functions of adrenalin 
seems to be just the opposite of the function of the insulin of 

1 Hormones are also called endocrines (en'do-krlnz), and the glands that secrete 
them are known as endocrine glands. 



CONTROL OF OUR BODIES 



603 



Adrenal 



Kidney 



the pancreas. It was stated, you will recall, that insulin 
makes it possible for the liver to store sugar. Now adrenalin, 
when it reaches the liver, causes sugar to be given out from 
the liver into the blood stream, and when the sugar reaches 
the muscles, this sugar affords a fuel from which energy may 
readily be released. Since the adrenals are especially active 
in secreting adrenalin, in case of emergency they are very 
essential to enable one to defend himself or to escape in case 
of danger. It is the extra secretion of adrenalin that enables 
a person to perform seemingly superhuman acts. The adre- 
nals are sometimes 
called the glands of 
combat, because they 
prepare one for a 
physical struggle. 
For instance, it is 
found that during a 
football game the 

amount of adrenalin . , , , , **** staes 

,, U1 , - ,, Adrenal glands 

in the blood of the 

players is enormously increased. Animals that are the most 
pugnacious have in proportion to the size of their bodies 
the largest adrenals. It is said that man has larger adrenals 
than any animal. No one can long survive the removal of 
the adrenals. 

The thyroid gland. The thyroid gland consists of two ma- 
roon-colored masses on either side of the neck above the 
windpipe and close to the larynx (111. p. 604). The secre- 
tion of this gland is known as thyroxin (thl-r5x'm). It is 
thyroxin that regulates the rate at which energy is released. 
It is therefore said to regulate the speed of living. That is, 
the more thyroxin one has, the more rapidly food materials 
are oxidized, and therefore the individual feels, thinks, and 




604 



MAN AND HIS ENVIRONMENT 



Voice box 



acts more quickly. An excessive development of the thy- 
roid gland, however, may lead to very serious results, and 
thyroid deficiency may give rise to even more serious con- 
sequences. 

In extreme cases the child that is deficient in thyroid 
secretion will never develop either physically or mentally 
and will be unable to recognize father or mother or show 

any interest in toys or any other 
objects. Experiments have been 
tried in feeding such children with 
thyroid extract. The results in 
some cases are said to be nothing 
short of marvelous. A child that 
was an idiot gradually became 
an apparently normal child. The 
only drawback is that the feeding 
of thyroid must always continue 
or the child will revert to the 
idiotic state. 

People suffering from the special 
type of idiocy which is due to the 
lack of thyroid secretion are known as cretins (kre'tmz). 
The word " cretin " means simple-minded. At the time 
the name " cretin " was first given, the cause of this type 
of feeble-mindedness was not known. One of the serious 
results of an overdeveloped thyroid gland is known as 
goiter. You may have seen persons having the front of the 
neck very much enlarged. This is due to an abnormal 
growth in an enlarged thyroid gland. If the goiter is not 
checked by skillful treatment, it may cause death. 

The pituitary gland. This is a tiny gland, no bigger than 
a pea, located in the human skull at the base of the brain. 
An account of the effects of one of the hormones from this 



Thyroid 



W/nt/p/pe 




After Stiles 



Thyroid gland 




Giant and dwarf 
Jim Tarver and Major Mite. What made the difference ? 



606 MAN AND HIS ENVIRONMENT 

small gland reads like some of the fairy stories with their 
tales of giants and pygmies. 

Have you ever seen the giants and dwarfs at a circus (111. 
p. 605) ? If you have, didn't you wonder what had caused 
them to differ so in size from yourself ? Would you suppose, 
however, that such a little body as the pituitary (pi-tu'i- 
ta-ri) gland might be responsible for a baby's remaining a 
child in size or developing the huge body of a giant? Yet 
this is just what seems to be true, for a certain part of the 
pituitary gland secretes a hormone known as tethelin (teth'e- 
lin) that promotes the growth of the skeleton. Therefore 
if a baby is born with an abnormally large pituitary gland, 
there will probably be an unusual amount of tethelin secreted, 
and as a result the child becomes a giant. If, on the other 
hand, this gland is deficient in size or in the amount of 
tethelin produced, the body fails to grow to normal size and 
may remain very small indeed. 

Experiments have been tried on young animals to show the 
effect of tethelin. The animals that were fed tethelin grew 
faster than those that were not fed this hormone. The 
experiments afford the hope that in the near future tethelin 
from animals may be used to promote the growth of babies 
that would otherwise become dwarfs. 

QUESTIONS AND APPLICATIONS 

1. Name five different systems of the human body. What is the prin- 
cipal function of each ? 

2. Show by examples why a sixth system is necessary. What is the 
function of this system? 

3. Observe a small child of about four years of age (or recall your own 
early experiences). Make a list of the activities that can be carried on 
during these early years. 

4. Name physical and mental activities that are now performed by you 
in about the same way as when you were a child. Enumerate additional 



CONTROL OF OUR BODIES 007 

specific activities in which you now engage that were impossible for you at 
the earlier age. Explain why this is possible. 

5. What are three possible subdivisions of the activities controlled by 
the nervous system ? Give examples of definite acts that might be classed 
under each subdivision. 

6. Name three principal parts of the nervous system. Where is each 
located ? 

7. Compare the nervous system and a telephone exchange. What are 
the essential parts of a complete action in the body and in telephoning? 

8. Define each of the following terms : receptor, afferent nerve, 
adjustor, efferent nerve, effector. 

9. Describe a neuron. How does a neuron differ from other cells of 
the body? 

10. In what respects do the messages that travel through our nervous 
system differ from those that pass over telephone wires ? 

1 1 . Describe the autonomic nervous system. Show how our emotions 
may affect the action of this system. 

12. Study the illustrations on pages 577 and 580 and describe the parts 
of the nervous system there shown. 

13. Supply the words needed to complete the following statements : 
If one should touch a hot stove, the (a) in the skin would receive the 

impression and transmit the message through the (6) nerves to the (c) mat- 
ter in the (d). Neurons in this region known as (e) would immediately 
transfer the message to the (/) nerves which would carry it back down the 
arm to the (g) in the (h). These would then (i) and the hand would be 
removed from danger. No pain would be felt, however, until the message 
had been sent through (j) nerves to the (k). 

When a cinder gets into the eye, the neurons known as (7) would be 
acted upon, and (m) nerves would send the message to the (n), when (o) 
would be felt. Neurons in the brain known as (p) would send out mes- 
sages along (q) nerves to the glands above the eyeball and (r) would be 
secreted. Other nerves would transmit impulses to the muscles that move 
the (s) and they would move over the (t). The various processes we have 
been describing are known as (u) action, and they are not under the con- 
trol of the (v). 

14. Describe the appearance of the brain as seen in surface view (p. 580) . 
What advantage is gained by the presence of convolutions ? 

15. Study 111. p. 581 and locate as many functions as you can in definite 
areas of the brain. See if vou can find out how these facts were determined. 



608 MAN AND HIS ENVIRONMENT 

16. What can you say of the possible connections that can be made 
from one part of the brain to another ? What proportion of these possible 
connections do you think most people employ ? What effect would vigor- 
ous physical and mental training have in utilizing more of these possi- 
bilities? 

17. Describe several of your experiences that would show that our daily 
acts are complicated procedures. 

18. Study the illustration on page 584 and state the resemblances and 
the differences in the eye and a camera. State clearly how " pictures " are 
formed and preserved by the help of each. 

19. What is meant by nearsightedness, farsightedness, and astigma- 
tism? How should each of these defects be corrected, and why should 
this correction be made ? 

20. Give rules for the proper care of the eyes. 

21. Study the illustration on page 587 and give a description of the 
various parts of the external, middle, and inner ear. 

22. Give an account of the way we keep our balance and become con- 
scious of sounds. 

23. Give specific directions for (a) removing earwax or an insect from 
the auditory canal ; (6) earache ; (c) running ear or gathering in the ear. 
What is mastoiditis and how is it caused ? 

24. Why are soldiers told to open their mouths when cannon are fired ? 
What is the effect on the tympanum (a) of going up in an airplane ? (b) of 
going into deep mines ? 

25. Locate and describe the organs that give us the sensations of touch, 
taste, smell, and pain. 

26. Show why proper food and fresh air are essential for the proper 
activity of the nervous system. 

27. Why must a healthy human body secure vigorous activity, relaxa- 
tion, and rest? 

28. Outline a daily program that would help much to insure health of 
body and mind. 

29. Make a list of various substances that should be classed as drugs. 
What is the striking difference in the effects of stimulants and narcotics ? 
Give several examples of each. To which class does alcohol belong? 

30. State three reasons why the taking of drugs, except under the direc- 
tion of a competent physician, is likely to prove harmful. 

31. Give as many reasons as you can for the wide divergence of opinion 
among people with reference to the use of alcohol. 



SUCCESS IN LIFE 609 

32. What objections to any use of alcohol are given by some of the 
eminent scientists and social workers? 

33. What decisive arguments against the use of alcoholic liquors by 
athletes are presented by trainers ? 

34. What new factors in modern life make the use of alcohol a greatly 
increased menace? 

35. What means of bodily control, other than that exerted by the 
nervous system, is now well known? 

36. Distinguish between secretin, insulin, adrenalin, thyroxin, and 
tethelin as to (a) their source, (b) their effects on bodily activities. Why 
are these substances known as (a) internal secretions, (6) as hormones? 

PROBLEM 3. UPON WHAT DOES SUCCESS IN LIFE 

DEPEND? 

What is meant by success in life ? If a youth were asked 
to name the one thing that he really desires most in life he 
would probably answer " Success." This answer, it is true, 
would not be a very definite one unless we knew the business 
or the profession in which the youth hoped to win success 
and the methods he would employ to secure it. But what- 
ever the final goal that is sought, every boy and girl would 
without doubt agree that success must necessarily include 
among other things the ability to do things that are worth 
while, and to get the largest real enjoyment out of life. 

The three factors of success in life. Dr. Walter in his 
book, Genetics, introduces a diagram (111. p. 610) that will 
well repay our study. Here we have each human life rep- 
resented as a three-sided affair, which Dr. Walter refers to as 
" the triangle of life." Since what we really are depends to 
so large an extent on our heritage, this factor is represented 
as the base of the triangle ; and this, as we notice, extends 
to a greater distance than does either of the other two sides. 
Our heritage, of course, can never be changed, since we can- 
not determine what we receive from our parents, grand- 



610 



MAN AND HIS ENVIRONMENT 



^"\ We J 



parents, and other more distant ancestors, who are countless 
in number. We should remember too that this factor of our 
being includes not only physical characteristics, such as color 
of hair or of eyes, complexion, relative tallness or shortness, 
but also mental capacity, and quite possibly moral tendencies. 
In the second place, each one of us is surrounded by an 
environment, which, as the diagram shows, includes what we 
have, or possess. The environment of a given person may 

be good, fair, or poor 
and so may be favor- 
able to success or un- 
favorable. Through- 
out the book we 
discussed some fea- 
tures of our environ- 
ment ; and as we 
have progressed in 
our study, we have 
learned how various plant and animal forms contribute to 
human welfare or retard it. The term " environment," 
like that of heritage, is a broad one. It includes not only 
earth, air, water, and various living things, but also a 
great variety of influences which may be ours if we will. 
Among these we should include the school, the church, the 
government, the wealth of experience that has come down 
to us through the records of history, literature, art, music, 
and the achievements of science. 

But unless we make the best possible use of these two 
factors, heritage and environment, real success in life will 
never be ours. It is true that we are not responsible in any 
way for the heritage we have received. We have also rela- 
tively little responsibility, at least during childhood and 
youth, for the environment in which we live. Each one of 



Heritage 

From Walter's "Genetics' 

The three factors involved in success 



SUCCESS IN LIFE 611 

us, however, unless he is below normal in mental ability, 
is rightly held to a strict responsibility for the third factor in 
the triangle of life ; namely, the response we make to the 
other two factors or, in other words, what we do. For exam- 
ple, one student in his high-school course, even though his 
inheritance and his environment may not be of the best, 
wins success because he puts forth his very best effort in 
training himself for life. For it is generally agreed that it is 
the successful effort put forth by the student that yields most 
in the educational process rather than the definite knowl- 
edge that may be acquired. On the other hand, another 
type of student fails, in spite of good heritage and good 
environment, because he persistently neglects the oppor- 
tunities that come to him. We shall later consider some- 
what more in detail each of these three factors that make or 
mar success. 

Success in life for the handicapped. Thus far in our 
discussion we have been considering the way of life for the 
average student who is not hampered by any serious physical 
or mental defect. In the Declaration of Independence it 
was written that " We hold these truths to be self-evident 
that all men are created equal, and that they are endowed by 
their Creator with certain inalienable Rights, that among 
these are Life, Liberty, and the pursuit of Happiness." 
This, of course, was a statement that had to do only with 
political rights. When, however, we consider this declara- 
tion from a biological point of view, we find that there is no 
equality as to heredity, environment, or response between 
any two human beings. Indeed, we need only to look about 
us to see that a considerable number of our fellow men have 
apparently a most unfortunate heredity, a very unfavorable 
environment, and that for these reasons, if for no other, their 
response is necessarily limited. 



612 



MAN AND HIS ENVIRONMENT 



There are, for instance, the blind, the deaf, the tubercular, 
the cripples, those who have weak hearts, and those who are 
either mentally defective or mentally ill. At first thought 

we might wonder if 
there are any oppor- 
tunities for success in 
life for those who are 
thus handicapped. 
But let us look for 
a moment on the 
other side of the pic- 
ture. Let us think 
of the victorious life 
of the blind and 
deaf Helen Keller 
(111. at left), the deaf 
Thomas Edison, the 
tuberculous Robert 
Louis Stevenson, the 
paralyzed Pasteur, 
and the multitude of 
heroes in everyday 
life who have been 
otherwise physically 
handicapped. What 
a debt we owe to 
these we have men- 
tioned and to count- 
less others who have faced life with all its discouragements 
and have won out ! In the paragraphs that follow we shall 
try to show you some of the ways in which success may 
be achieved by those who are handicapped in one way or 
another. 




Photograph by Courtesy of American Foundation for the Blind, Inc. 

" One comes to value perseverance where one 
sees what difficulties vanish before it." 
Message prepared and photograph autographed by 
Miss Keller for this book. Helen Keller reading the 
lips of her teacher, Mrs. Anne Sullivan Macy. 



SUCCESS IN LIFE 613 

The education of the blind. Were you to visit Perkins 
Institution or any other similar school for the blind, you 
would marvel at the possibilities for the training of those with 
defective vision. There you would see those who were de- 
prived of sight carrying on practically all of the school activ- 

abcdefghij 

• #••••• •• •• • • • 

• •••••••••• 

klmnopqrst 

• ••••••••••• • • 

• •••••••••• 

u v w x y z 

• • •••••• 

• •• • • 



! ( ) "? 



» * * 



# • •• •• •• •• •• • • 

• • ••••••• •• 

Numeral Sign » Capital Sign 

1234567890 

• • •• •• • •• •• • • • 

• •••••••••• 

Courtesy of Perkins Institution 

The Braille alphabet 
Each of these dots is raised in the books they read. 

ities of the seeing child. Because of lack of vision special 
methods for these children are essential. Of chief interest 
is their method of reading, for these children are finger- 
readers rather than eye-readers. Letters on their pages are 
formed by combinations of raised dots (Braille, bral) (111. 
above) and a special device is provided which enables them 



614 MAN AND HIS ENVIRONMENT 

to write (see 111. p. 613) and to use figures. The Institution 
offers a complete course of study from the kindergarten 
through the high school, a number of their graduates going 
on to college. 

In addition to their academic studies they become skilled 
in such crafts as weaving, caning chairs, and making mat- 
tresses. The one fine art in which these boys and girls excel 
is music, and therefore much emphasis is placed on this kind 
of training. They also engage in athletics. The boys may 
be seen on the football field and track, and both boys and 
girls have regular gymnasium classes, and all enjoy the swim- 
ming pool. Were these young people to attempt to do their 
work in the ordinary school classes they would find it almost 
impossible. But guided by their specially trained teachers, 
these blind students often become remarkably successful in 
their later life. 

The education of the deaf. At the Clarke School for the 
Deaf in Northampton, Massachusetts, the visitor would be 
astonished in following the successful methods there devel- 
oped from the kindergarten through the eighth grade, 
preparatory to entering high schools with hearing boys and 
girls. He would see little children, deaf from birth, taught 
to understand words by watching the movements of the 
teacher's lips, and even to repeat the words they have never 
heard. The development of a sense of rhythm brings 
pleasure to these young people. By means of sound-amplify- 
ing instruments the quality of the voice and the pronun- 
ciation are improved. In all classes recitations are conducted 
by the teachers in an ordinary tone of voice, the pupils 
reading the teacher's lips and giving the answers almost as 
in an ordinary classroom. The graduates of the school are 
usually able to adjust themselves to life and to make their 
way in it with a remarkable degree of success (111. p. 612). 



SUCCESS IN LIFE 



015 



The education of the crippled. It is estimated that there 
are over 100,000 persons in the State of New York alone who 
are so seriously crippled that life for them is exceedingly 
difficult. No one can speak more feelingly on this subject 
than can President Franklin Delano Roosevelt, who has 
himself battled so tri- 
umphantly with this 
handicap (111. at right). 
He speaks as follows : 
" A wheel-chair cripple 
is not only a dead load 
on the earning power 
of a community, but in 
most cases requires the 
attention and the care 
of some able-bodied per- 
son. Modern medical 
science has advanced to 
such a point that in a 
great majority of cases 
these cripples can be 
made to function. It 

is Often a long and Photographby New York.Times Studio 

~ Autographed for this book 

COStly procedure, but it Franklin Delano Roosevelt 

is WOrth while for the Thirty-second President of the United States. 

various communities 

and the state to spend this time and money, for it will be 

repaid a thousand fold." 

" The surest way to benefit the cripple is to help him to 
achieve the best there is in him by encouraging and stim- 
ulating his own efforts. Pity is the last thing in the world 
the self-respecting cripple wants. What he wants is the 
chance to make the most of what he has and to stand on his 




616 MAN AND HIS ENVIRONMENT 

own feet." x This courageous attitude toward physical 
handicaps should be taken by every one who finds life diffi- 
cult. (See Miss Keller's message, page 612.) At this Insti- 
tute the visitor finds those who have lost the use of arms and 
legs taught drafting, commercial art, printing, jewelry mak- 
ing, welding, left-hand penmanship, leathercraft, office prac- 
tice, and other useful employments. The spirit of the 
whole institution is well expressed in the title and the con- 
tents of its monthly publication, " Thumbs Up." 2 

Education of the feeble-minded and the mentally ill. 
First we must call attention to the difference between these 
two classes of the mentally handicapped. By feeble-mind- 
edness we mean a condition from birth which renders the 
child or the adult below the average as to mental capacity. 
Three grades are now recognized : (1) the idiot is an in- 
dividual who has only the average ability throughout life of 
most children one to three years of age. No matter how 
long he may live he will hardly be able to wash, or dress, or 
feed himself. (2) The imbecile is one whose mental life is 
that of a child of three to seven years of age. He can, of 
course, accomplish more than can an idiot, but he will con- 
stantly be in need of care. (3) The moron's abilities continue 
throughout life to be about those of an individual of eight 
to twelve years. It is most important that these feeble- 
minded members of the human race be discovered early in 
life, that they be given special training, and especially that 
they be prevented from having children ; for feeble-minded- 
ness is very likely to be passed on from one generation to 
another. If, however, these handicapped children are given 

1 The statements just quoted are found in a pamphlet entitled "The Cripple 
Finds Himself," issued by the Institute for the Crippled and Disabled (New York 
City). 

2 Copies may be obtained from the Institute for the Crippled and Disabled, 
400 First Avenue, New York City. 



SUCCESS IN LIFE 617 

the special training for which they are fitted, many of them 
become self-supporting and useful citizens. 

In contrast with feeble-mindedness, mental illness (com- 
monly called insanity) is usually not hereditary. It is fre- 
quently the result of great worry or of some mental shock, and 
it is usually curable, if proper treatment is given. Un- 
fortunately most people who are thus afflicted, and their 
friends as well, object strongly to seeking treatment in a 
hospital for mental illness. They think that entrance to 
these institutions casts a shadow over their whole lives. 
If they could but know what wonderful treatment is given 
there, and how many of the patients recover, they would 
feel no more hesitance about seeking help in a mental hospital 
than about entering an ordinary hospital for physical ail- 
ments. Great progress has been made in recent years in 
the treatment of mental illness, and it is most important 
that those who are thus afflicted should have the help of 
doctors and nurses who have had expert training. In these 
special hospitals, not only is the patient given the rest, the 
food, and the other treatment that is needed, but he is also 
taught a new way of carrying on his life in such a way that 
he may escape future attacks. His time is occupied with 
pleasurable games and other activities, and he often looks 
back upon the associations he has made with real pleasure. 

The great importance of education. Certainly enough 
has been said to show the tremendous consequences that 
come from good and from bad heritage. Most of us, however, 
belong to a great middle class, a class in which heritage is 
neither exceptionally good nor strikingly bad. For this 
reason, in order to win success, each one of us must do all 
in his power to make the two factors of environment and 
response count for all they are worth. Hence the great 
importance of getting a good education. 



618 



MAN AND HIS ENVIRONMENT 



" Education is something more than going to school for a 
few weeks each year, is more than knowing how to read and 
write. It has to do with character, with industry, and with 
patriotism. Education tends to do away with vulgarity, 
pauperism, and crime, tends to prevent disease and dis- 
grace, and helps to manliness, success, and loyalty." 1 




Autographed for this boot 



The four Taft brothers 
New York City owes a great debt to Henry W. Taft, who was chairman of the com- 
mittee which first established the city high schools in 1897. William H. Taft was 
the 27th President of the United States and later Chief Justice of the Supreme Court. 
Charles P. Taft was owner of the " Cincinnati Times-Star." Horace D. Taft is the 
head of the Taft School for boys in Connecticut. Their father was Secretary of War 
and afterwards Attorney General of the United States in President Grant's adminis- 
tration; Minister to Austria, 1882-1884; and Minister to Russia, 1884-1885. 



1 Quoted from "Jukes-Edwards," by Dr. A. E. Winship. 
of New England Journal of Education. 



Used by permission 



SUCCESS IN LIFE 619 

" The school is not the end but only the beginning of an 
education. Yet its place cannot be filled in any other way. 
The best thing the millions of our youth can do to assure their 
future success is to work faithfully at their studies. That 
opportunity for improvement and discipline will never re- 
turn." — Calvin Coolidge. 




Men have always reverenced prodigious inborn gifts, and- 
always will. Indeed, barbarous men always say of the possessors of 
such gifts: These are not men, they are gods. But we tonchers who 
carry on a system of popular education, which is by far the most com- 
plex and valuable invention of this century, know that we have to do, 
not with the highly gifted units, but with the millions who are more 
or less capable of being cultivated by the long, patient, artificial 
training called education. For us and our system, the genius is no 
standard, but the 'cultivated man' is. To his stature we and many 
of our pupils may in time attain. 



Dr. Charles W. Eliot, President of Harvard University for forty years 

This message to high-school students was prepared for this book and signed when 

Dr. Eliot was ninety-one years old. 

Self-activity as an essential condition for success. True 

success in life is not a gift that can be bestowed by anyone 
on another, no matter how rich or talented the would-be 
giver may be. It is something that must be won ; and in 
order to win it, each individual must meet certain demands. 
For instance, that the body may be developed as perfectly 
as possible, suitable food and an abundance of fresh air must 
be supplied, and physical activities of different kinds must be 
engaged in. That the mind may be trained, it is important 
that the youth attend school and apply himself actively in 
the work of the classroom. In all these activities he must 
heartily cooperate with the parent and the teacher if he is 



620 MAN AND HIS ENVIRONMENT 

to become successful in the work he is to undertake in life 
whether that work be that of a physician, a lawyer, a mer- 
chant, a teacher, a skilled mechanic, or a leader of any sort. 
Why are all these activities essential? 

In the human body there are five hundred separate muscles, 
and each of these muscles must be trained to do its share in 
the work of life. Now each muscle is controlled by the brain 
or by other parts of the nervous system (see pp. 570-583), 
in which there are billions of nerve cells and fibers. All 
these nerve cells must be taught to cooperate, and this 
comes only as a result of long training. 

Every one knows that actions which are repeated again 
and again are carried out more effectively. The reason for 
this is that, by using repeatedly certain nerve and muscle 
cells, we are in a certain sense making beaten tracks through 
our bodies, somewhat as a path through deep snow is finally 
made by the repeated tramping of feet. Training, whether 
in athletics, in mathematics, or in manual work, can come 
only by doing definite tasks over and over again. In this 
way habits are formed so that at length we seem to do a great 
many things, like walking, riding the bicycle, and playing 
the piano, without any conscious thought. 

To win athletic success, a boy cheerfully lets cigarettes 
and candy severely alone, goes to bed early, and drives him- 
self through weeks of tiresome training. Likewise, a girl 
who wishes to become a skilled pianist will practice hour 
after hour. Many school tasks seem irksome and useless; 
but if a youth is to succeed in school, in college, or in life, 
these tasks must be done ; and the more cheerfully they 
can be performed, the better the training which is thereby 
secured. 

It is most important that a youth seek the kind of training 
for which he is naturally adapted. Undoubtedly certain 






SUCCESS IN LIFE 621 

boys are better fitted for activities that bring into play 
the large muscles than for making the mental effort nec- 
essary to prepare for college. Such boys should pursue the 
courses in agriculture, commercial branches, or technical 
science. For girls, too, there are many opportunities for 
special training that will fit them to win success in household 
science, clerical work, or technical pursuits. Too much 
emphasis cannot be laid on the fact that only when boys 
and girls are absorbed in healthful pleasure or in useful pur- 
suits are they on the road to success. 

The supreme importance of habits. Most people, when 
they speak of habits, seem to regard them as something to 
be shunned or deplored. True it is that a considerable 
number of human habits of thought and action belong 
to this class. As examples we may cite the habits of 
eating rapidly, of excessive smoking, of drinking intoxi- 
cating liquors, and of acting from motives of selfishness 
and greed. 

As Professor James puts it, " The hell to be endured here- 
after, of which theology tells, is no worse than the hell we 
make for ourselves in this world by habitually fashioning 
our characters in the wrong way. Could the young but 
realize how soon they will become mere walking bundles of 
habits, they would give more heed to their conduct while in 
the plastic state. We are spinning our own fates, good or 
evil, and never to be undone. Every smallest stroke of 
virtue or of vice leaves its never-so-little scar. The drunken 
Rip Van Winkle, in Jefferson's play, excuses himself for every 
fresh dereliction by saying, ' I won't count this time.' 
Well ! he may not count it, and a kind Heaven may not 
count it ; but it is being counted none the less. Down among 
his nerve cells and fibers the molecules are counting it, 
registering and storing it up to be used against him when the 



622 MAN AND HIS ENVIRONMENT 

next temptation comes. Nothing we ever do is in strict 
scientific literalness wiped out." x 

But in reality habits are, or should be, our greatest friends and 
allies. Suppose it were necessary for us to take conscious 
thought every time we took a step, or wrote a word, or struck 
a key on the piano ! " A man might be occupied all day in 
dressing and undressing himself ; the attitude of the body 
would absorb all his attention and energy ; the washing of 
his hands, or the fastening of a button would be as difficult to 
him on each occasion as to the child on his first trial ; and 
he would furthermore be completely exhausted by his exer- 
tions. Think of the pains necessary to teach a child to stand, 
of the many efforts which it must take, and of the ease with 
which it stands at last, unconscious of any effort." 2 

As a further example of the domination of everyday acts 
by the habits that are acquired, Professor James cites the 
following : " ' Habit a second nature ! Habit is ten times 
nature ! ' the Duke of Wellington is said to have exclaimed ; 
and the degree to which this is true no one can appreciate as 
well as one who is a veteran soldier himself. The daily drill 
and the years of discipline end by fashioning a man com- 
pletely over again as to most of the possibilities of his con- 
duct." In the World War it was astonishing to see how 
soon the " rookies " who came into camp utterly unaccus- 
tomed to military discipline learned the routine, and then 
crossed the ocean to do their full share on the battlefields of 
France and Belgium. 

The laws of habit formation. Since habits play such an 
important part in the lives of each one of us, how can we 
acquire those habits that make for our advantage and well- 

1 From Psychology by William James. Used by permission of Henry Holt and 
Company, publishers. 

2 Ibid. 



SUCCESS IN LIFE 623 

being? Can we find some general principles that will help 
us to make such habits our permanent possession ? 

In the first place, it is much easier to form habits in youth, 
when, as James says, " the nervous system is in the plastic 
state." Just as it is difficult to plow a new path through 
snow that has settled down and hardened, so too an adult 
finds it very difficult to acquire a new habit or to uproot an 
old one. It is for this reason that the home and the school 
become such important factors in habit formation. The 
parent and the teacher realize far more than can the growing 
boy or girl how vital to success in life are habits of neatness, 
of prompt obedience, of courtesy, and of honesty. And it is 
because of this knowledge that they labor so earnestly to 
make habits like these a part of the very being of those for 
whom they are responsible. 

Again, suppose we desire to form a new habit, like getting 
up promptly in the morning or showing real courtesy to our 
parents. What would be the effect of launching out upon 
the venture with as much vigor and enthusiasm as an athlete 
shows in training for a boat race or a ball game ? If we keep 
everlastingly at it, even though like the athlete we are beaten 
now and then, what are the chances for final success? Is 
there any other way of plowing the right paths through our 
nerve cells that will mean success in the end? It is worth 
while to remind ourselves now and again that good resolu- 
tions are futile and powerless until they are translated into 
action. 

Once more, it is most important to remember that we must 
never make an exception — never say, as did Rip Van Winkle, 
" I won't count this time " — in our new resolves, before the 
habit we have set out to acquire has become so firmly fixed in 
our nervous system that it has become second nature. In 
breaking a habit, like that of smoking, for example, the same 



624 MAN AND HIS ENVIRONMENT 

rule must be applied. It is surprising how soon a desire to 
do the wrong thing will die out if it is never fed. 

And finally, we should remember that " the great thing in 
all education is to make our nervous system our ally instead of 
our enemy. For this reason we must make automatic and 
habitual as early as possible as many useful actions as we 
can, and guard against growing into ways that are likely to 
be harmful to us, as we would guard against the plague. 
The more of the details of our daily lives we can hand over to 
the effortless direction of habit, the more our higher powers 
of mind will be free for their own proper work," and so help 
to win the success for which we are striving. 

" Let no youth have any anxiety about the upshot of his 
education, whatever the line of it may be. If he keep faith- 
fully busy each hour of the day, he may safely leave the 
final result to itself. He can with perfect certainty count on 
waking up some fine morning to find himself one of the com- 
petent ones of his generation, in whatever pursuit he may 
have singled out." 1 

QUESTIONS AND APPLICATIONS 

1. Ask yourself what your greatest ambition in life is at the present 
time. What ambition was uppermost in your mind a few years ago? 
What has brought about this change in your thought ? 

2. Why do biologists emphasize heritage as the predominating factor 
in life ? Of what diverse elements does heritage consist ? 

3. In what ways do the home, the school, the town or city, the country, 
foreign countries, and even the heavenly bodies have more or less definite 
influence upon us ? 

4. For which of the three factors of success are we most responsible? 
Decide for yourself ways in which you can make this factor of more influ- 
ence in your life than you are now doing. 

1 From Psychology by William James. Used by permission of Henry Holt and 
Company, publishers. 



SUCCESS IN LIFE 625 

5. Who wrote the Declaration of Independence ? Show different ways 
in which this statement as to the equality of human beings is not true, bio- 
logically speaking. 

6. Study the biographies of Helen Keller, Thomas Edison, Theodore 
Roosevelt, Franklin D. Roosevelt, Robert Louis Stevenson, Louis Pas- 
teur, and Charles Darwin. In what ways were these leaders of thought 
and action seriously handicapped ? How did each win success in spite of 
handicaps ? 

7. Why is it necessary for handicapped children to have special train- 
ing? Describe methods that are now used in the education of the blind, 
the deaf, the crippled, and the mentally ill. 

8. Remembering what we learned on pages 579-583, discuss the ways 
in which we form our habits. Show why habits (both good and bad) are 
of such tremendous importance in life. 

9. Give three specific principles that should be borne in mind in the 
formation of right habits. 

10. From your study of biology thus far what do you consider the 
gravest dangers that threaten the human race? What can mankind do 
to meet these dangers? 

1 1 . Enumerate as many ways as you can in which biological researches 
and their applications may contribute to Human Welfare. 



SUGGESTED LIST OF REFERENCE BOOKS 
IN BIOLOGY 

The lists marked A below contain the titles of books recom- 
mended as a first choice for a small reference library. Many of 
them are adapted for use by the student, and most of them are 
relatively inexpensive. The 5-lists enumerate titles of additional 
books which will be found very useful in biological study. The 
prices are taken from the United States Catalog. While they 
are subject to change, they are inserted to give the teacher some 
idea of the cost of each book. 

General Biology 
A-List 

Caldwell, Otis W., Skinner, C. E., and Tietz, N. W. — Bio- 
logical Foundations of Education; Ginn & Company. $2.72. 

Carpenter, Kathleen E. — Life in Inland Waters; The Macmil- 
lan Company. $4.50. 

de Kruif, Paul — Microbe Hunters; Harcourt, Brace & Com- 
pany. $3.50. 

Downing, Eliot R. — Our Living World; Longmans, Green & 
Company. $2.00. 

Locy, William A. — Biology and Its Makers; Henry Holt & 
Company, Inc. $3.00. 

Mann, Paul B., and Hastings, George T. — Out of Doors; 
Henry Holt & Company, Inc. $1.60. 

Park, William H., and Williams, Anna W. - — Who's Who 
among the Microbes; The Century Company. $3.00. 

Woodruff, L. L. — Foundations of Biology; The Macmillan 
Company. $3.50. 

B-List 

Caldwell, Otis W., and Slosson, Edward E. — Science Remak- 
ing the World; Garden City Publishing Company. $1.00. 

Cannon, Walter B. — Bodily Changes in Pain, Hunger, Fear, 
and Rage; D. Appleton Company. $3.00. 

626 



SUGGESTED LIST OF REFERENCE BOOKS 627 

Castle, W. E. — Genetics and Eugenics; Harvard University 
Press. $3.00. 

Comstock, Anna B. — Handbook of Nature Study; Comstock 
Publishing Company. $4.00. 

Locy, William A. — Growth of Biology ; Henry Holt & Company, 
Inc. $4.00. 

Morgan, Ann H. — Field Book of Ponds and Streams; G. P. 
Putnam's Sons. $3.50. 

Thompson, J. Arthur — The New Natural History, 3 volumes ; 
G. P. Putnam's Sons. $18.00. 

Vallery-Radot, Rene — Life of Pasteur ; Garden City Pub- 
lishing Company. $1.00. 

Walter, H. E. — Genetics, 3d Edition ; The Macmillan Com- 
pany. $2.50. 

Wilson, E. B. — Cell in Development and Heredity, 3d Edition ; 
The Macmillan Company. $9.00. 

Plant Biology 

A-List 

Clements, Frederic E., and Edith W. — Rocky Mountain- 
Flowers; H. W. Wilson Company. $3.50. 
Conn, H. W. — Bacteria, Yeasts and Molds, 3d Revised Edition ; 

Ginn & Company. $1.60. 
Gager, C. Stuart — Fundamentals of Botany; P. Blakiston's 

Son & Company. $2.00. 
Ganong, W. F. — The Living Plant; Henry Holt & Company, 

Inc. $2.50. 
Harwood, W. S. — New Creations in Plant Life; The Macmillan 

Company. $2.00. 
Keeler, Harriet L. — Our Native Trees and How to Identify 

Them; Charles Scribner's Sons. $3.00. 
Keeler, Harriet L. — Our Northern Shrubs and How to Identify 

Them; Charles Scribner's Sons. $3.00. 
Mathews, F. Schuyler — Field Book of American Wild Flowers; 

G. P. Putnam's Sons. $3.50. 

B-List 

Campbell, D. H. — An Outline of Plant Geography; The Mac- 
millan Company. $4.00. 

Durand, Herbert — Field Book of Common Ferns; G. P. Put- 
nam's Sons. $2.50. 



628 SUGGESTED LIST OF REFERENCE BOOKS 

Gager, C. Stuart — General Botany; P. Blakiston's Son & Com- 
pany. $4.00. 

Mathews, F. Schuyler — Field Book of American Trees and 
Shrubs; G. P. Putnam's Sons. $3.50. 

Osterhout, W. J. V. — Experiments with Plants; The Macmil- 
lan Company. $2.00. 

Pack, Charles L., and Gill, Tom — Forest Facts for Schools; 
The Macmillan Company. $.80. 

Parsons, Frances T. Dana — How to Know the Wild Flowers; 
Charles Scribner's Sons. $3.00. 

Parsons, Frances T. Dana — How to Know the Ferns; Charles 
Scribner's Sons. $2.50. 

Peterson, Maud G. — How to Know the Wild Fruits; The Mac- 
millan Company. $2.00. 

Sargent, Frederick Leroy — Plants and Their Uses ; Henry 
Holt & Company, Inc. $1.60. 

Transeau, Edgar N. — Science of Plant Life; World Book 
Company. $1.68. 

Animal Biology 
A- List 

Chapman, Frank M. — Bird-Life; D. Appleton & Company. 

$5.00. 
Hegner, Robert — College Zoology, 3d Edition ; The Macmillan 

Company. $3.50. 
Henderson, Junius — The Practical Value of Birds ; The Mac- 
millan Company. $2.50. 
Herrick, Glenn W. - — Insects Injurious to the Household and 

Annoying to Man; The Macmillan Company. $3.00. 
Hornaday, William T. — American Natural History; Charles 

Scribner's Sons. $5.00. 
Howard, L. O. — Insect Menace; The Century Company. $3.50. 
Jordan, David Starr, Kellogg, Vernon, and Heath, Harold 

— Animals; D. Appleton & Company. $2.50. 
Lutz, Frank E. — Field Book of Insects, Revised Edition ; G. P. 

Putnam's Sons. $3.50. 

B-List 

Chapman, Frank M. — Handbook of Birds of Eastern North 
America; D. Appleton & Company. $5.00. 

Dickerson, Mary C. — Frog Book; Doubleday, Doran & Com- 
pany, Inc. $5.00. 



SUGGESTED LIST OF REFERENCE BOOKS 629 

Ditmars, Raymond — Reptiles of the World; The Macmillan 

Company. $4.00. 
Forbush, Edward H. — Birds of Massachusetts and Other New 

England States; Massachusetts Board of Agriculture. $5.00. 
Holland, W. J. — The Butterfly Book; Doubleday, Doran & 

Company, Inc. $10.00. 
Holmes, S. J. — Biology of the Frog, 4th Revised Edition ; The 

Macmillan Company. $2.75. 
Hornaday, William T. — Minds and Manners of Wild Animals; 

Charles Scribner's Sons. $2.50. 
Howard, L. O. — Fighting the Insects; The Macmillan Company. 

$2.50. 
Jordan, David Starr, and Everman, B. W. — American Food 

and Game Fishes; Doubleday, Doran & Company, Inc. $5.00. 
Metcalf, Z. P. — Textbook of Economic Zoology; Lee, Febiger. 

$4.00. 
Myers, Harriet W. — Western Birds; The Macmillan Company. 

$3.00. 
Weed, Clarence M., and Dearborn, Ned — Birds in Their 

Relation to Man; J. B. Lippincott Company. $3.50. 
Wheeler, William Morton — Social Life among the Insects; 

Harcourt, Brace & Company. $4.00. 

Human Biology 
A-List 

American Medical Association — Nostrums and Quackery. 
$1.00. 

Bolduan, Charles F. — Public Health and Hygiene; W. B. 
Saunders Company. $2.75. 

Broadhurst, Jean — Home and Community Hygiene; J. B. Lip- 
pincott Company. $3.00. 

Clodd, Edward — The Childhood of the World; The Macmillan 
Company. $1.25. 

Ditmars, R